Correct Answer: (B) Entomology

Explanation

Entomology is the branch of Zoology that deals with the scientific study of insects. Scientists who study insects are known as entomologists. The field covers insect classification, anatomy, behaviour, ecology, physiology, and their economic importance.

Exam Facts

• Entomology is the scientific study of insects, a branch of Zoology.
• Apis (honey bee), Bombyx mori (silkworm), Anopheles (malaria mosquito), and Culex (filaria mosquito) are important insects frequently asked in competitive exams.
• Apiculture is the rearing of honey bees, while Sericulture is the rearing of silkworms for silk production.
• Arachnology is the study of spiders and scorpions, whereas Entomology deals only with insects.

Correct Answer: (A) Binary

Explanation

The Binary Number System (base-2) is the fundamental number system used in computers and digital electronics. It uses only two digits: 0 and 1, which correspond to the OFF (0) and ON (1) states of electronic circuits. Since computers process data electronically, all instructions and data are ultimately represented in binary form.

Exam Facts

• Binary Number System has base 2 and uses only 0 and 1.
• Decimal Number System has base 10 (digits 0–9) and is used in everyday calculations.
• Octal Number System has base 8 (digits 0–7), while the Hexadecimal Number System has base 16 (digits 0–9 and A–F); both are commonly used as shorthand representations of binary data.
• 1 Byte = 8 Bits, where a bit (Binary Digit) is the smallest unit of data in a computer.

• Common binary conversions:
  • 1 KB = 1024 Bytes
  • 1 MB = 1024 KB
  • 1 GB = 1024 MB
  • 1 TB = 1024 GB

Correct Answer: (C) Nitrogen

Explanation

Nitrogen (N₂) is the most abundant gas in the Earth’s atmosphere, constituting about 78% of its volume. It is a relatively inert gas and plays a crucial role in the nitrogen cycle, which is essential for the growth of plants and the survival of living organisms.

Exam Facts

• Nitrogen (N₂) makes up about 78% of the Earth’s atmosphere.
• Oxygen (O₂) is the second most abundant gas, constituting about 21%, and is essential for respiration and combustion.
• Argon (Ar) is the third most abundant gas in the atmosphere, accounting for about 0.93% (more abundant than carbon dioxide and neon).
• Carbon dioxide (CO₂) constitutes about 0.04% of the atmosphere and is an important greenhouse gas responsible for the greenhouse effect.
• Approximate composition of dry air:
  • Nitrogen: 78.08%
  • Oxygen: 20.95%
  • Argon: 0.93%
  • Carbon dioxide: ~0.04%

Correct Answer: (A) Anemometer

Explanation

An Anemometer is an instrument used to measure the speed (velocity) of wind. It is widely used in meteorological observatories, weather forecasting stations, airports, and environmental studies. The most common type is the cup anemometer, which measures wind speed by the rotation of cups mounted on horizontal arms.

Exam Facts

• Anemometer measures wind speed, while a Wind Vane measures wind direction.
• A Barometer measures atmospheric pressure (invented by Evangelista Torricelli).
• A Manometer measures the pressure of gases or liquids in a closed system.
• A Thermometer measures temperature; common types include mercury and digital thermometers.
• Other important scientific instruments frequently asked in exams:
  • Hygrometer – Measures humidity.
  • Rain Gauge – Measures rainfall.
  • Seismograph – Records earthquake waves.
  • Altimeter – Measures altitude.
  • Hydrometer – Measures the relative density (specific gravity) of liquids.

Correct Answer: (A) Tin

Explanation

Bronze is an alloy primarily made by mixing copper and tin. It is harder, stronger, and more resistant to corrosion than pure copper. The discovery of bronze marked the beginning of the Bronze Age, when it was extensively used for making tools, weapons, statues, and utensils.

Exam Facts

• Bronze is an alloy of Copper (Cu) and Tin (Sn).
• Brass is an alloy of Copper and Zinc (Zn) and is commonly used in musical instruments and decorative items.
• Solder is generally an alloy of Tin and Lead, used for joining electrical components.
• Steel is an alloy of Iron and Carbon, while Stainless Steel contains Iron, Chromium, Nickel, and Carbon.
• Important alloys frequently asked in exams:
  • Bell Metal – Copper + Tin
  • German Silver (Nickel Silver) – Copper + Zinc + Nickel (contains no silver)
  • Duralumin – Aluminium + Copper + Magnesium + Manganese
  • Gun Metal – Copper + Tin + Zinc

Correct Answer: (C) Anopheles mosquito

Explanation

Malaria is transmitted to humans through the bite of an infected female Anopheles mosquito. The disease is caused by Plasmodium parasites, mainly Plasmodium falciparum and Plasmodium vivax in India. The mosquito acts as the vector (carrier), while humans are the primary hosts.

Exam Facts

• Female Anopheles mosquito transmits malaria, caused by Plasmodium parasites.
• Aedes aegypti mosquito transmits Dengue, Chikungunya, Yellow Fever, and Zika Virus.
• Culex mosquito transmits Filariasis (Elephantiasis) and Japanese Encephalitis.
• The malarial parasite was discovered by Alphonse Laveran (1880), while the role of the Anopheles mosquito in transmitting malaria was discovered by Sir Ronald Ross (1897), who received the Nobel Prize in Physiology or Medicine (1902).
• Common human malaria parasites include Plasmodium falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi.

Correct Answer: (A) NaCl

Explanation

Common salt is Sodium Chloride (NaCl), an ionic compound formed by the combination of sodium (Na⁺) and chloride (Cl⁻) ions. It is widely used in food, preservation, medicine, and various industrial processes. Common salt is obtained mainly by evaporation of seawater and by mining rock salt.

Exam Facts

• NaCl (Sodium Chloride) is the chemical formula of common salt.
• CaCO₃ (Calcium Carbonate) is found in limestone, marble, chalk, and shells.
• Na₂CO₃ (Sodium Carbonate) is known as washing soda and is used in glass, soap, and detergent industries.
• Na₃PO₄ (Trisodium Phosphate) is used in cleaning agents, water treatment, and detergents.
• Important sodium compounds frequently asked in exams:
  • NaHCO₃ – Baking Soda
  • NaOH – Caustic Soda
  • Na₂CO₃·10H₂O – Washing Soda
  • NaCl – Common Salt

Correct Answer: (C) Kidney

Explanation

The kidneys are the primary organs responsible for filtering and purifying blood. They remove metabolic wastes, excess salts, and excess water to form urine, while maintaining the body’s fluid, electrolyte, and acid-base balance. Each healthy human has two kidneys, located on either side of the vertebral column.

Exam Facts

• The functional unit of the kidney is the Nephron, with each kidney containing about 1 million nephrons.
• The kidneys remove urea, uric acid, creatinine, excess water, and salts from the blood to form urine.
• The hormone Erythropoietin (EPO) is produced by the kidneys and stimulates the production of red blood cells (RBCs).
• The kidneys also help regulate blood pressure through the Renin–Angiotensin–Aldosterone System (RAAS).
• Functions of the other options:
  • Pancreas – Produces insulin, glucagon, and digestive enzymes.
  • Intestines – Responsible for digestion and absorption of nutrients.
  • Stomach – Secretes hydrochloric acid (HCl) and digestive enzymes for food digestion.

Correct Answer: (D) Plastids

Explanation

Plastids are membrane-bound cell organelles found only in plant cells and algae. The most important plastid is the chloroplast, which contains chlorophyll and performs photosynthesis. Other plastids include chromoplasts (store pigments) and leucoplasts (store food such as starch, oils, and proteins).

Exam Facts

• Plastids are found only in plant cells and algae; they are absent in animal cells.
• Chloroplasts contain chlorophyll and are the site of photosynthesis.
• Types of plastids:
  • Chloroplasts – Green; photosynthesis.
  • Chromoplasts – Yellow, orange, or red pigments.
  • Leucoplasts – Store starch, oils, and proteins.
• Nucleus, mitochondria, and Golgi apparatus are present in both plant and animal cells.
• Other distinguishing features of plant cells:
  • Cell wall made of cellulose.
  • Large central vacuole.
  • Plastids (including chloroplasts) for photosynthesis.

Correct Answer: (C) Sulphur

Explanation

Sulphur (S) is a non-metal belonging to Group 16 (Chalcogens) of the Periodic Table. It is a yellow, brittle solid at room temperature and is a poor conductor of heat and electricity. In contrast, Mercury, Zinc, and Copper are all metals.

Exam Facts

• Sulphur (S) is a non-metal with atomic number 16 and belongs to Group 16 of the Periodic Table.
• Mercury (Hg) is the only metal that is liquid at room temperature (Gallium and Caesium melt near room temperature but are normally solids).
• Copper (Cu) is an excellent conductor of electricity and is widely used in electrical wiring.
• Zinc (Zn) is used for galvanization to prevent rusting of iron and steel.
• Common properties of non-metals:
  • Poor conductors of heat and electricity (except graphite).
  • Brittle and non-sonorous.
  • Generally do not possess metallic lustre (except iodine).

Correct Answer: (D) Carrot

Explanation

Carrot is a root vegetable because the edible part is its taproot, which stores food for the plant. It is rich in beta-carotene, which is converted into Vitamin A in the human body and is essential for healthy vision and immunity.

Exam Facts

• Carrot is a taproot and is an excellent source of beta-carotene (Provitamin A).
• Cauliflower is a flower (inflorescence) vegetable.
• Cucumber and gourd are fruit vegetables, as they develop from the flower’s ovary.
• Other important edible plant parts:
  • Potato – Stem tuber
  • Ginger – Rhizome (modified stem)
  • Onion – Bulb
  • Sweet potato – Tuberous root
• Examples of root vegetables frequently asked in exams include Carrot, Radish, Turnip, Beetroot, and Sweet Potato (modified root).

Correct Answer: (B) Typhoid

Explanation

Typhoid is a water-borne and food-borne disease caused by the bacterium Salmonella typhi. It spreads through contaminated water or food and is common in areas with poor sanitation and unsafe drinking water.

Exam Facts

• Typhoid is caused by Salmonella typhi and spreads through contaminated food and water.
• Malaria is a vector-borne disease transmitted by the female Anopheles mosquito and is caused by Plasmodium parasites.
• Tuberculosis (TB) is caused by Mycobacterium tuberculosis and spreads through airborne droplets from infected persons.
• Diphtheria is caused by Corynebacterium diphtheriae and spreads through respiratory droplets or close contact.
• Other important water-borne diseases include:
  • Cholera – Vibrio cholerae
  • Hepatitis A & E – Hepatitis A and E viruses
  • Amoebiasis – Entamoeba histolytica
  • Giardiasis – Giardia lamblia

Correct Answer: (A) AC (Alternating Current)

Explanation

Nikola Tesla is best known for developing the Alternating Current (AC) electrical system, which became the standard for electricity generation, transmission, and distribution worldwide. His inventions, including the polyphase AC system and the AC induction motor, made long-distance transmission of electricity efficient and economical. Tesla’s AC system ultimately prevailed over Thomas Edison’s Direct Current (DC) system in the famous “War of Currents.”

Exam Facts

• Nikola Tesla developed the Alternating Current (AC) power system and invented the AC induction motor.
• Thomas Alva Edison promoted the Direct Current (DC) electrical system.
• AC current changes its direction periodically (in India, the standard frequency is 50 Hz), making it suitable for long-distance power transmission.
• DC current flows in only one direction and is commonly supplied by batteries and cells.
• The SI unit of electric current is the ampere (A), named after the French physicist André-Marie Ampère.

Correct Answer: (A) Crocodile

Explanation

A Crocodile is a reptile, not an amphibian. It belongs to the class Reptilia and has dry, scaly skin, breathes through lungs throughout its life, and lays amniotic eggs on land. In contrast, frogs, salamanders, and newts belong to the class Amphibia, whose members generally live both on land and in water.

Exam Facts

• Crocodile belongs to the class Reptilia, while Frog, Salamander, and Newt belong to the class Amphibia.
• Amphibians have moist, glandular skin, undergo metamorphosis, and can respire through skin, lungs, and gills (during the larval stage).
• Reptiles have dry, keratinized scales, breathe only through lungs, and lay shelled (amniotic) eggs on land.
• Examples of Amphibians: Frog, Toad, Salamander, Newt, Caecilian.
• Examples of Reptiles: Crocodile, Lizard, Snake, Turtle, Tortoise.

Explanation

A gas can be liquefied by compression only below its critical temperature because, at this temperature, the intermolecular attractive forces become effective enough to bring the gas molecules closer together, causing them to condense into a liquid. Above the critical temperature, the kinetic energy of the molecules is too high for compression alone to liquefy the gas.

Exam Facts

• Critical Temperature is the highest temperature at which a gas can be liquefied by applying pressure alone.
• Intermolecular forces (such as Van der Waals forces) are responsible for the liquefaction of gases.
• The Critical Pressure is the minimum pressure required to liquefy a gas at its critical temperature.
• The Critical Point is the combination of critical temperature and critical pressure, beyond which the distinction between liquid and gas disappears.
• Important gas laws:
  • Boyle’s Law: Pressure is inversely proportional to volume at constant temperature.
  • Charles’s Law: Volume is directly proportional to absolute temperature at constant pressure.
  • Avogadro’s Law: Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Explanation

Ethylene (C₂H₄) is a natural plant hormone that promotes the ripening of fruits. It accelerates processes such as softening, color change, conversion of starch into sugars, and the development of aroma. Commercially, ethylene gas is used in controlled ripening chambers for fruits like bananas, mangoes, tomatoes, and apples.

Exam Facts

• Ethylene (C₂H₄) is the only gaseous plant hormone and promotes fruit ripening.
• Fruits such as banana, mango, papaya, tomato, and apple are climacteric fruits that ripen in response to ethylene.
• Calcium carbide, once illegally used for artificial ripening, is harmful to human health because it may contain toxic impurities such as arsenic and phosphorus compounds.
• Other important plant hormones:
  • Auxin – Promotes cell elongation.
  • Gibberellin – Promotes stem elongation and seed germination.
  • Cytokinin – Promotes cell division.
  • Abscisic Acid (ABA) – Induces dormancy and closes stomata during water stress.
• Methane, chlorine gas, and isopropyl alcohol are not used for fruit ripening.

Correct Answer: (C) Becquerel

Explanation

The SI unit of radioactivity is the Becquerel (Bq). One becquerel represents one radioactive disintegration (decay) per second. It is named after the French physicist Henri Becquerel, who discovered natural radioactivity in 1896.

Exam Facts

• Becquerel (Bq) is the SI unit of radioactivity, where 1 Bq = 1 nuclear disintegration per second.
• Curie (Ci) is the older, non-SI unit of radioactivity; 1 Curie = 3.7 × 10¹⁰ Becquerels.
• Henri Becquerel discovered natural radioactivity in 1896, while Marie and Pierre Curie discovered the radioactive elements Polonium and Radium.
• The SI unit of absorbed radiation dose is the Gray (Gy), and the SI unit of equivalent/effective radiation dose is the Sievert (Sv).
• Other important SI units:
  • Ampere (A) – Electric current
  • Volt (V) – Electric potential difference
  • Watt (W) – Power
  • Joule (J) – Energy

Correct Answer: (D) Nephrons

Explanation

The nephron is the structural and functional (filtration) unit of the kidney. Each human kidney contains about 1 million nephrons, which filter blood, remove metabolic wastes, and form urine while maintaining the body’s water, electrolyte, and acid-base balance.

Exam Facts

• Nephron is the structural and functional unit of the kidney.
• A nephron consists of Bowman’s capsule, glomerulus, proximal convoluted tubule (PCT), Loop of Henle, distal convoluted tubule (DCT), and collecting duct.
• Ultrafiltration of blood takes place in the glomerulus inside Bowman’s capsule.
• Ureter carries urine from the kidney to the urinary bladder, while the urethra carries urine from the urinary bladder to the outside of the body.
• Neuron is the structural and functional unit of the nervous system, not the kidney.

Correct Answer: (B) Use of fuse

Explanation

A fuse is a safety device connected in series with an electrical circuit. It contains a thin wire of low melting point that melts when excessive current flows due to overloading or short-circuiting, thereby breaking the circuit and protecting electrical appliances from damage and fire hazards.

Exam Facts

• A fuse protects electrical appliances from overloading and short-circuiting by breaking the circuit when excessive current flows.
• A fuse wire is made of an alloy with a low melting point and high resistivity, commonly tin and lead.
• MCB (Miniature Circuit Breaker) is a modern replacement for the fuse and automatically trips during overloading or short circuits.
• Earthing protects people from electric shock by providing a low-resistance path for leakage current to the ground; it does not protect against overloading.
• A stabilizer protects appliances from voltage fluctuations, while an electric meter measures electrical energy consumption in kilowatt-hours (kWh).

Correct Answer: (C) H₂O vapour

Explanation

Water vapour (H₂O vapour) is the most abundant greenhouse gas in the Earth’s atmosphere. It naturally contributes the largest share of the greenhouse effect by absorbing and re-emitting infrared radiation, thereby helping to maintain the Earth’s temperature. Although carbon dioxide (CO₂) is the most important long-lived greenhouse gas influenced by human activities, water vapour is the most abundant greenhouse gas overall.

Exam Facts

• Water vapour (H₂O vapour) is the most abundant greenhouse gas in the atmosphere.
• Major greenhouse gases include Water Vapour (H₂O), Carbon Dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), Ozone (O₃), and Chlorofluorocarbons (CFCs).
• Carbon monoxide (CO) is not considered a major greenhouse gas, although it indirectly influences atmospheric chemistry.
• Methane (CH₄) has a much higher global warming potential than CO₂ over a 100-year period, but it is present in much smaller concentrations.
• Major sources of greenhouse gases:
  • CO₂ – Burning of fossil fuels and deforestation.
  • CH₄ – Rice fields, livestock, wetlands, and landfills.
  • N₂O – Nitrogen fertilizers and industrial activities.
  • H₂O vapour – Natural evaporation from oceans, lakes, rivers, and transpiration from plants.

Correct Answer: (C) Indole Acetic Acid

Explanation

Indole-3-Acetic Acid (IAA) is the principal natural auxin, a plant growth hormone that promotes cell elongation, root initiation, apical dominance, and tropic movements. It is synthesized mainly in the shoot tips and young leaves and plays a vital role in the overall growth and development of plants.

Exam Facts

• Indole-3-Acetic Acid (IAA) is the most important natural auxin and promotes cell elongation and plant growth.
• Auxins are produced mainly in the shoot apex, young leaves, and developing seeds.
• Chlorophyll is the green pigment responsible for photosynthesis, not a plant growth hormone.
• Other important plant hormones:
  • Gibberellins (GA) – Promote stem elongation, flowering, and seed germination.
  • Cytokinins – Stimulate cell division and delay leaf senescence.
  • Abscisic Acid (ABA) – Inhibits growth, induces seed dormancy, and closes stomata during water stress.
  • Ethylene – A gaseous hormone that promotes fruit ripening and leaf abscission.
• Phenylacetic Acid (PAA) is also an auxin-like compound but is less active than Indole Acetic Acid (IAA) and is not regarded as the principal plant growth hormone.

Correct Answer: (B) Nitrates and nitrites

Explanation

Plants absorb nitrogen from the soil mainly in the form of nitrate (NO₃⁻) and, to a lesser extent, nitrite (NO₂⁻) ions. In practice, plants also absorb ammonium (NH₄⁺), but since it is not given as an option, “Nitrates and nitrites” is the correct answer. Nitrogen is essential for the synthesis of proteins, nucleic acids (DNA & RNA), chlorophyll, and enzymes.

Exam Facts

• Plants primarily absorb nitrogen as nitrate (NO₃⁻) and ammonium (NH₄⁺) ions; in this question, nitrates and nitrites is the closest correct option.
• Atmospheric nitrogen (N₂) cannot be used directly by most plants and must first be converted into usable forms through the nitrogen cycle.
• Nitrogen-fixing bacteria such as Rhizobium (in leguminous plants) and Azotobacter convert atmospheric nitrogen into plant-available compounds.
• Nitrogen is a major component of amino acids, proteins, nucleic acids, ATP, and chlorophyll.
• Deficiency of nitrogen causes stunted growth and yellowing of older leaves (chlorosis) due to reduced chlorophyll production.

Correct Answer: (A) 64

Explanation

The relationship between vapour density (VD) and molecular weight (molar mass) is:

Molecular Weight = 2 × Vapour Density

Therefore,

Molecular Weight = 2 × 32 = 64

Hence, the correct answer is 64.

Exam Facts

• Formula: Molecular Weight = 2 × Vapour Density (VD).
• Vapour Density (VD) is defined as the ratio of the mass of a given volume of a gas to the mass of an equal volume of hydrogen under the same conditions of temperature and pressure.
• Molar Mass (Molecular Weight) is expressed in g/mol.
• According to Avogadro’s Law, equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
• Common examples:
  • O₂: Molecular weight = 32, Vapour density = 16
  • CO₂: Molecular weight = 44, Vapour density = 22
  • N₂: Molecular weight = 28, Vapour density = 14
  • SO₂: Molecular weight = 64, Vapour density = 32

Correct Answer: (C) Amylase

Explanation

The first enzyme that mixes with food in the human digestive tract is salivary amylase (Ptyalin), which is secreted by the salivary glands in the mouth. It begins the digestion of starch (carbohydrates) by converting it into maltose and dextrins.

Exam Facts

• Salivary amylase (Ptyalin) is the first digestive enzyme to act on food and starts carbohydrate digestion in the mouth.
• Pepsin is secreted by the stomach and digests proteins into smaller peptides.
• Trypsin is secreted by the pancreas (in the form of trypsinogen) and acts in the small intestine to digest proteins.
• Humans do not produce cellulase; therefore, cellulose cannot be digested by the human digestive system.
• Other important digestive enzymes:
  • Lipase – Digests fats into fatty acids and glycerol.
  • Maltase – Converts maltose into glucose.
  • Lactase – Converts lactose into glucose and galactose.
  • Sucrase (Invertase) – Converts sucrose into glucose and fructose.

Correct Answer: (D) H₂O molecules

Explanation

When sodium chloride (NaCl) dissolves in water, it dissociates into Na⁺ and Cl⁻ ions. The Na⁺ ions become surrounded by water (H₂O) molecules in a process called hydration. The oxygen end of the water molecule, which carries a partial negative charge (δ⁻), is attracted to the positively charged Na⁺ ion.

Exam Facts

• NaCl is an ionic compound and dissociates into Na⁺ and Cl⁻ ions in water.
• The process in which water molecules surround dissolved ions is called hydration.
• Around a Na⁺ ion, the oxygen atom (δ⁻) of water faces the ion, while around a Cl⁻ ion, the hydrogen atoms (δ⁺) of water face the ion.
• Water is called a universal solvent because its polar nature enables it to dissolve many ionic and polar substances.
• A solution of NaCl in water conducts electricity because it contains free-moving ions, making it an electrolyte.

Correct Answer: (C) Starch

Explanation

The iodine test is used to detect the presence of starch. When a few drops of iodine solution are added to a starch-containing solution such as rice water, it forms a blue-black complex with the amylose component of starch. This characteristic colour confirms the presence of starch.

Exam Facts

• Iodine solution gives a blue-black colour in the presence of starch.
• Benedict’s solution and Fehling’s solution are used to test for reducing sugars such as glucose.
• Biuret reagent gives a violet colour in the presence of proteins.
• Sudan III/IV stain or the grease spot test is used to detect fats (lipids).
• Starch is a polysaccharide made up of amylose and amylopectin and serves as the storage carbohydrate in plants.

Correct Answer: (A) Water

Explanation

During photosynthesis, the oxygen (O₂) released by green plants comes from the photolysis (splitting) of water (H₂O) during the light reaction. Sunlight breaks water molecules into oxygen, hydrogen ions, and electrons. The released oxygen diffuses into the atmosphere, while the hydrogen is used in the formation of glucose.

Exam Facts

• Oxygen released during photosynthesis originates from water (H₂O), not from carbon dioxide.
• Photolysis of water occurs in the thylakoid membranes of chloroplasts during the light reaction.
• The overall equation of photosynthesis is:
  
  6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂
  
• Chlorophyll is the green pigment that absorbs sunlight and is located in the chloroplasts.
• The fact that the released oxygen comes from water was conclusively demonstrated by Samuel Ruben and Martin Kamen (1941) using the oxygen-18 (¹⁸O) isotope.

Correct Answer: (A) Aedes mosquito

Explanation

Dengue is transmitted by the female Aedes mosquito, mainly Aedes aegypti. It is caused by the Dengue virus (DENV) and spreads through the bite of an infected mosquito. The mosquito usually bites during the daytime, especially in the early morning and late afternoon.

Exam Facts

• Dengue is caused by the Dengue virus and is transmitted by the female Aedes aegypti mosquito.
• Aedes mosquitoes also transmit Chikungunya, Zika virus disease, and Yellow Fever.
• Female Anopheles mosquito transmits Malaria, while Culex mosquito transmits Filariasis (Elephantiasis) and Japanese Encephalitis.
• The Aedes mosquito breeds in clean, stagnant water found in containers, flower pots, tyres, coolers, and overhead tanks.
• Common symptoms of dengue include high fever, severe headache, muscle and joint pain (“breakbone fever”), skin rash, and low platelet count (thrombocytopenia).

Correct Answer: (C) 40

Explanation

The percentage of calcium in Calcium Carbonate (CaCO₃) is calculated using its molar mass.

• Atomic mass of Ca = 40
• Atomic mass of C = 12
• Atomic mass of O = 16 × 3 = 48

Molar mass of CaCO₃ = 40 + 12 + 48 = 100

Percentage of Calcium:
$$\frac{40}{100} \times 100 = 40\%$$

Hence, the percentage of calcium in CaCO₃ is 40%.

Exam Facts

• Calcium Carbonate (CaCO₃) has a molar mass of 100 g/mol.
• It contains 40% Calcium (Ca), 12% Carbon (C), and 48% Oxygen (O) by mass.
• CaCO₃ is the chief constituent of limestone, marble, chalk, and seashells.
• On heating, CaCO₃ decomposes into Calcium Oxide (CaO) and Carbon Dioxide (CO₂):
  • CaCO₃ → CaO + CO₂
• Calcium is essential for the formation of bones and teeth, blood clotting, muscle contraction, and nerve impulse transmission.

Correct Answer: (D) Na⁺ and Zn²⁺

Explanation

A transition metal ion is one that has a partially filled d-orbital in its atom or in at least one of its common oxidation states.

• Na⁺ has the electronic configuration 1s² 2s² 2p⁶ and no d-electrons, so it is not a transition metal ion.
• Zn²⁺ has the electronic configuration 3d¹⁰, with a completely filled d-subshell, so it is not considered a transition metal ion.
• Fe²⁺ (3d⁶) and Co³⁺ (3d⁶) have partially filled d-orbitals and are therefore transition metal ions.

Exam Facts

• Transition elements are the d-block elements that have partially filled d-orbitals in their atoms or in at least one of their oxidation states.
• Iron (Fe) and Cobalt (Co) are transition metals because they form ions with incomplete d-orbitals.
• Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are not regarded as transition elements because their atoms and common ions have completely filled d¹⁰ configurations.
• Transition metals commonly exhibit:
  • Variable oxidation states
  • Formation of coloured compounds
  • Complex ion formation
  • Catalytic properties
• Examples of electronic configurations:
  • Fe²⁺ → 3d⁶
  • Co³⁺ → 3d⁶
  • Zn²⁺ → 3d¹⁰
  • Na⁺ → Neon (Ne) configuration (no d-electrons)

Correct Answer: (B) Fusion reactions of hydrogen atoms forming helium

Explanation

The Sun produces energy through nuclear fusion occurring in its core. Under extremely high temperature (about 15 million K) and pressure, hydrogen nuclei (protons) fuse together to form helium, releasing a tremendous amount of energy according to Einstein’s equation, E = mc². This energy reaches the Earth as solar radiation (light and heat).

Exam Facts

• Solar energy is produced by the nuclear fusion of hydrogen into helium in the Sun’s core.
• In the proton–proton (pp) chain reaction, four hydrogen nuclei combine to form one helium nucleus, releasing energy.
• The energy released is due to the conversion of a small amount of mass into energy, explained by Einstein’s mass-energy equivalence equation (E = mc²).
• Nuclear fusion powers the Sun and other stars, whereas nuclear fission is used in nuclear reactors on Earth.
• The Sun’s core has an approximate temperature of 15 million Kelvin, which provides the conditions necessary for fusion reactions.

Correct Answer: (A) Nickel and Chromium

Explanation

Stainless steel is an alloy of iron containing chromium (at least 10.5%) and often nickel. Chromium forms a thin, protective chromium oxide layer on the surface, making stainless steel highly resistant to rust and corrosion, while nickel improves its strength, toughness, and corrosion resistance.

Exam Facts

• Stainless steel is mainly an alloy of Iron (Fe), Chromium (Cr), and Nickel (Ni), with a small amount of carbon.
• Chromium provides corrosion and rust resistance by forming a protective oxide layer on the surface.
• Nickel enhances the strength, toughness, ductility, and corrosion resistance of stainless steel.
• Common alloys frequently asked in competitive exams:
  • Brass – Copper + Zinc
  • Bronze – Copper + Tin
  • German Silver – Copper + Zinc + Nickel (contains no silver)
  • Duralumin – Aluminium + Copper + Magnesium + Manganese
• Stainless steel is widely used in kitchen utensils, surgical instruments, construction materials, chemical industries, and food-processing equipment due to its durability and corrosion resistance.

Correct Answer: (C) PVC

Explanation

PVC (Polyvinyl Chloride) is the most commonly used insulating material for electrical wires. It is an excellent electrical insulator, flexible, durable, moisture-resistant, and inexpensive. PVC prevents leakage of electric current and protects users from electric shock.

Exam Facts

• PVC (Polyvinyl Chloride) is widely used as an insulating material for electrical wires and cables.
• An ideal electrical insulator should have high electrical resistance, good mechanical strength, heat resistance, and moisture resistance.
• Other commonly used insulating materials include rubber, porcelain, glass, mica, bakelite, and Teflon.
• Graphite is a good conductor of electricity because it has free electrons, so it is not used as an insulator.
• Sulfur is a non-metal and a poor conductor, but it is not commonly used for coating electrical wires due to its unsuitable mechanical properties.

Correct Answer: (D) 31 pairs

Explanation

Humans have 31 pairs of spinal nerves that arise from the spinal cord. These are mixed nerves, containing both sensory (afferent) and motor (efferent) fibers, and they connect the spinal cord with different parts of the body.

Exam Facts

• Humans have 31 pairs of spinal nerves:
  • 8 Cervical (C1–C8)
  • 12 Thoracic (T1–T12)
  • 5 Lumbar (L1–L5)
  • 5 Sacral (S1–S5)
  • 1 Coccygeal (Co1)
• There are 12 pairs of cranial nerves, which arise directly from the brain.
• Spinal nerves are mixed nerves, carrying both sensory (afferent) and motor (efferent) impulses.
• The spinal cord extends from the medulla oblongata to approximately the L1–L2 vertebral level in adults.
• The central nervous system (CNS) consists of the brain and spinal cord, while the peripheral nervous system (PNS) includes the cranial nerves, spinal nerves, and ganglia.

Correct Answer: (B) Potential difference

Explanation

In a parallel combination of resistors, each resistor is connected directly across the same two terminals of the power source. Therefore, the potential difference (voltage) across each resistor remains the same, while the current divides among the different branches according to their resistances.

Exam Facts

• In a parallel circuit, the potential difference (voltage) across each branch is equal.
• The current divides among the branches, and the total current is the sum of the branch currents:
  • I = I₁ + I₂ + I₃ + …
• The equivalent resistance of resistors in parallel is always less than the smallest individual resistance.
• Formula for equivalent resistance in parallel:
  • 1/R = 1/R₁ + 1/R₂ + 1/R₃ + …
• In contrast, in a series circuit, the current remains the same through all resistors, while the voltage is divided among them.

Correct Answer: (B) Graphite

Explanation

Graphite is an allotrope of carbon and is an exception among non-metals because it conducts electricity. Each carbon atom in graphite forms three covalent bonds, leaving one free (delocalized) electron per atom. These free electrons can move freely between the layers, enabling graphite to conduct electricity.

Exam Facts

• Graphite is the only common non-metal that conducts electricity due to the presence of delocalized electrons.
• Diamond is another allotrope of carbon but is an excellent electrical insulator because all four valence electrons of each carbon atom are involved in strong covalent bonds.
• Sulphur is a typical non-metal and is a poor conductor of heat and electricity.
• Graphite is used in electrodes, electric motors, batteries, lubricants, and pencil leads.
• Important allotropes of carbon:
  • Diamond – Hardest natural substance; electrical insulator.
  • Graphite – Soft, slippery, good conductor of electricity.
  • Fullerene (C₆₀) – Spherical “buckyball” molecule with applications in nanotechnology.
  • Graphene – A single layer of graphite; an excellent conductor with exceptional strength.

Correct Answer: (A) Raman Effect

Explanation

Sir Chandrasekhara Venkata (C. V.) Raman discovered the Raman Effect on 28 February 1928. The Raman Effect refers to the change in the wavelength (or frequency) of light when it is scattered by molecules. This discovery laid the foundation for Raman Spectroscopy, an important analytical technique used in chemistry, physics, medicine, and material science. C. V. Raman was awarded the Nobel Prize in Physics in 1930, becoming the first Asian scientist to receive a Nobel Prize in the sciences.

Exam Facts

• C. V. Raman discovered the Raman Effect in 1928 and received the Nobel Prize in Physics (1930).
• 28 February is celebrated every year as National Science Day in India to commemorate the discovery of the Raman Effect.
• Raman Spectroscopy is widely used to identify chemical compounds and molecular structures.
• X-rays were discovered by Wilhelm Conrad Röntgen in 1895, not by C. V. Raman.
• C. V. Raman was awarded India’s highest civilian honour, the Bharat Ratna, in 1954 and was the first Indian Director of the Indian Institute of Science (IISc), Bengaluru.

Correct Answer: (A) Hafnium Carbide (HfC)

Explanation

Hafnium Carbide (HfC) is one of the most heat-resistant known materials. It has an extremely high melting point of about 3,900°C, making it suitable for applications involving very high temperatures, such as rocket nozzles, hypersonic vehicles, and spacecraft heat shields.

Exam Note: Some modern scientific studies identify Tantalum Hafnium Carbide (Ta₄HfC₅) as having an even higher melting point than pure HfC. However, in competitive examinations, Hafnium Carbide (HfC) is the accepted answer when it appears among the options.

Exam Facts

• Hafnium Carbide (HfC) is an ultra-high-temperature ceramic (UHTC) with a melting point of around 3,900°C.
• Tantalum Hafnium Carbide (Ta₄HfC₅) is considered one of the highest melting materials known, with a melting point of about 4,200°C.
• Titanium is valued for its high strength, low density, and corrosion resistance, but it is not the most heat-resistant material.
• Tungsten (W) has the highest melting point among pure metals (3,422°C) and is widely used in high-temperature applications.
• Ultra-high-temperature ceramics such as HfC, TaC, and ZrC are used in rocket engines, missile nose cones, thermal protection systems, and aerospace components.

Correct Answer: (B) Professor Greg Herman

Explanation

Professor Greg Herman of Oregon State University (USA) led the development of transparent contact lens sensors capable of monitoring stress hormones, uric acid, glucose, and intraocular pressure (IOP) associated with glaucoma. These smart contact lenses use transparent biosensors embedded in the lens to continuously analyze biomarkers present in tear fluid, enabling non-invasive health monitoring.

Exam Facts

• Professor Greg Herman is a chemical engineering professor at Oregon State University who led the development of these transparent biosensors.
• The smart contact lenses can monitor glucose, stress hormones, uric acid, and intraocular pressure (IOP) using tear fluid.
• Glaucoma is caused by damage to the optic nerve, often associated with increased intraocular pressure, and is one of the leading causes of irreversible blindness.
• Tear fluid is a promising, non-invasive diagnostic medium because it contains several biomarkers that reflect a person’s health status.
• Smart contact lenses are an important application of wearable biosensor technology, enabling continuous, real-time health monitoring without the need for frequent blood tests.

Correct Answer: (D) Technical University of Munich

Explanation

Scientists at the Technical University of Munich (TUM), Germany, developed a holographic imaging process that uses the radiation emitted by a standard Wi-Fi router to generate three-dimensional (3D) images of the surrounding environment. The technology uses one fixed and one movable antenna to record Wi-Fi signals and reconstruct 3D images through holographic processing. It has potential applications in Industry 4.0, search-and-rescue operations, robotics, and indoor object tracking.

Exam Facts

• The technology was developed by researchers at the Technical University of Munich (TUM), Germany.
• The principal researchers were Dr. Friedemann Reinhard and Philipp Holl, and their work was published in Physical Review Letters in 2017.
• The system works with ordinary commercial Wi-Fi routers and can reconstruct 3D images without modifying the transmitter.
• Possible applications include tracking objects in factories (Industry 4.0), indoor navigation, robotics, and locating victims trapped under collapsed buildings or avalanches.
• The technique can also work with Bluetooth and mobile phone signals, since they are based on similar electromagnetic wave principles.

Correct Answer: (A) Standard Cosmological Model

Explanation

SCM stands for Standard Cosmological Model, also known as the ΛCDM (Lambda–Cold Dark Matter) Model. It is the widely accepted model that explains the origin, evolution, structure, and expansion of the Universe. According to this model, the Universe began with the Big Bang about 13.8 billion years ago and is currently undergoing accelerated expansion due to dark energy.

Exam Facts

• SCM stands for Standard Cosmological Model (ΛCDM Model).
• According to the model, the Universe is composed of approximately 5% ordinary matter, 27% dark matter, and 68% dark energy.
• The model is based on the Big Bang Theory, according to which the Universe originated about 13.8 billion years ago.
• The Cosmic Microwave Background (CMB) is regarded as strong observational evidence supporting the Standard Cosmological Model.
• The Λ (Lambda) in the ΛCDM Model represents the cosmological constant (dark energy), while CDM stands for Cold Dark Matter.

Correct Answer: (B) Beauty quark

Explanation

The LHCb (Large Hadron Collider beauty) experiment is one of the major experiments at the Large Hadron Collider (LHC). It is specifically designed to study the beauty (bottom or b) quark and particles containing it. The experiment investigates the differences between matter and antimatter (CP violation) and searches for evidence of new physics beyond the Standard Model.

Exam Facts

• LHCb stands for Large Hadron Collider beauty, where “beauty” refers to the beauty (bottom or b) quark.
• The experiment is located at CERN (European Organization for Nuclear Research) near Geneva, on the France–Switzerland border.
• The beauty quark is also known as the bottom (b) quark and is one of the six fundamental quarks: up, down, charm, strange, top, and bottom (beauty).
• One of the primary goals of LHCb is to study CP (Charge-Parity) violation, which helps explain why the Universe contains more matter than antimatter.
• The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator, housing four major experiments:
  • ATLAS
  • CMS
  • ALICE
  • LHCb

Correct Answer: (B) Robodoc

Explanation

ROBODOC is a computer-assisted robotic surgical system designed for orthopaedic surgeries, particularly hip and knee replacement (joint replacement) procedures. It assists surgeons in precisely preparing the bone for implant placement, resulting in greater accuracy, improved implant alignment, and better long-term outcomes.

Exam Facts

• ROBODOC was the first active robotic system approved for orthopaedic surgery, especially hip and knee replacement.
• It uses computer-assisted planning and robotic precision to improve the accuracy of bone cutting and implant positioning.
• Benefits of robotic-assisted joint replacement include:
  • Greater surgical precision
  • Better implant alignment
  • Reduced damage to surrounding tissues
  • Faster recovery in many patients
• LAPRODOC is not a standard robotic system used for hip or knee replacement surgery.
• Other well-known surgical robotic systems include:
  • da Vinci Surgical System – Minimally invasive general, urological, and gynecological surgeries.
  • MAKO Robotic System – Robotic-assisted hip and knee replacement.
  • CyberKnife – Robotic radiosurgery for treating tumors without conventional surgery.

Correct Answer: (A) Mesentery

Explanation

The mesentery is a double fold of the peritoneum that attaches the intestines to the posterior abdominal wall. In 2016–2017, after research led by Professor J. Calvin Coffey of the University of Limerick (Ireland), it was recognized as a continuous structure and classified as an organ, often referred to in competitive exams as the 79th organ of the human body.

Exam Facts

• The mesentery supports and anchors the small and large intestines to the abdominal wall.
• It serves as a passage for blood vessels, lymphatic vessels, nerves, and fat supplying the intestines.
• Recognition of the mesentery as a distinct organ has improved the understanding and treatment of abdominal and gastrointestinal diseases.
• Adenoids are lymphoid tissues located in the nasopharynx and are part of the immune system.
• Colon is a part of the large intestine, while the vulva refers to the external female genitalia; neither is regarded as the “79th organ.”

Correct Answer: (B) 630

Explanation

The human body contains about 630 skeletal muscles (often stated as around 600–650 muscles in anatomy textbooks). These muscles are responsible for body movement, posture, joint stability, and heat production. Therefore, the closest correct answer is 630.

Exam Facts

• The human body has approximately 630 skeletal muscles (commonly quoted as about 600–650 muscles).
• There are 206 bones in the adult human body.
• The three types of muscles are:
  • Skeletal (Voluntary/Striated) – Attached to bones and responsible for body movements.
  • Smooth (Involuntary/Unstriated) – Found in the walls of internal organs such as the stomach and intestines.
  • Cardiac Muscle – Found only in the heart; involuntary and striated.
• The largest muscle in the human body is the Gluteus Maximus.
• The longest muscle is the Sartorius, while the strongest muscle (by force exerted) is generally considered the Masseter (jaw muscle).

Correct Answer: (D) Stapedius Muscle

Explanation

The Stapedius is the smallest skeletal muscle in the human body, measuring about 1 mm in length. It is located in the middle ear and is attached to the stapes (stirrup) bone, the smallest bone in the human body. Its function is to stabilize the stapes and protect the inner ear from excessively loud sounds by reducing the movement of the stapes (acoustic reflex).

Exam Facts

• Stapedius is the smallest muscle in the human body.
• It is located in the middle ear and is attached to the stapes, the smallest bone in the human body.
• The largest muscle in the human body is the Gluteus Maximus.
• The longest muscle is the Sartorius, which runs from the hip to the inner side of the knee.
• The Masseter is regarded as the strongest muscle in terms of the force it can generate during chewing.

Correct Answer: (C) Finger nails

Explanation

Human hair and finger nails are both primarily composed of keratin, a tough, fibrous structural protein. Keratin provides strength, durability, and protection to hair and nails. Therefore, hair is made of the same substance as finger nails.

Exam Facts

• Hair and nails are composed mainly of hard keratin, a fibrous protein.
• Keratin is also found in the outer layer of the skin (epidermis), but hair and nails contain a harder form of keratin.
• Teeth are mainly composed of:
  • Enamel – the hardest substance in the human body, made primarily of hydroxyapatite (calcium phosphate).
  • Dentin – located beneath the enamel.
• The outermost layer of the skin is the epidermis, which contains keratinized cells that protect the body from injury, pathogens, and water loss.
• Human hair grows from hair follicles located in the dermis and grows at an average rate of about 1 cm per month.

Correct Answer: (A) Cylindrical lens

Explanation

Astigmatism is a refractive error caused by an irregular curvature of the cornea or, less commonly, the lens. As a result, light rays do not focus at a single point on the retina, causing blurred or distorted vision. It is corrected using a cylindrical lens, which compensates for the uneven curvature and focuses light properly on the retina.

Exam Facts

• Astigmatism is corrected with a cylindrical lens.
• Other common refractive errors:
  • Myopia (Short-sightedness) – Corrected by a concave (diverging) lens.
  • Hypermetropia (Long-sightedness) – Corrected by a convex (converging) lens.
  • Presbyopia – Usually corrected with bifocal or progressive lenses.
• Astigmatism can occur along with myopia or hypermetropia.
• The cornea provides most of the eye’s focusing power, while the lens fine-tunes the focus through accommodation.
• The retina contains:
  • Rods – Responsible for vision in dim light.
  • Cones – Responsible for colour vision and sharp vision.

Correct Answer: (A) It is a medical diagnostic test.

Explanation

An angiogram (or angiography) is a medical diagnostic imaging test used to examine the inside of blood vessels, especially arteries. During the procedure, a contrast dye is injected into the blood vessels, and X-ray imaging (fluoroscopy) is used to detect blockages, narrowing, aneurysms, or other abnormalities.

Exam Facts

• Angiography is commonly used to diagnose coronary artery disease (CAD), blockages, aneurysms, and other vascular disorders.
• A contrast dye (contrast medium) is injected into the blood vessels before taking X-ray images.
• Coronary angiography specifically examines the arteries supplying blood to the heart.
• If a significant blockage is detected during coronary angiography, doctors may perform angioplasty and place a stent to restore blood flow.
• Related medical imaging techniques:
  • ECG (Electrocardiogram) – Records the electrical activity of the heart.
  • Echocardiography (Echo) – Uses ultrasound to assess the heart’s structure and function.
  • MRI (Magnetic Resonance Imaging) – Uses magnetic fields and radio waves to create detailed images of internal organs.
  • CT Scan (Computed Tomography) – Uses X-rays to produce cross-sectional images of the body.

Correct Answer: (B) McNaughton test

Explanation

The McNaughton (M’Naghten) Test is not a medical diagnostic test. It is a legal test used in criminal law to determine whether an accused person can be held criminally responsible for their actions based on the insanity defence. It assesses whether the person understood the nature of the act or knew that it was wrong at the time of the offence.

Exam Facts

• M’Naghten (McNaughton) Test is a legal standard, not a medical diagnostic procedure. It is used to assess the insanity defence in criminal cases.
• Colonoscopy is an endoscopic procedure used to examine the colon (large intestine) and detect conditions such as polyps, colorectal cancer, ulcers, and inflammation.
• Doppler Test (Doppler Ultrasound) uses high-frequency sound waves to evaluate blood flow through arteries and veins and helps diagnose vascular disorders.
• CT Scan (Computed Tomography) uses X-rays and computer processing to produce detailed cross-sectional images of internal organs, bones, and blood vessels.
• Common diagnostic imaging techniques frequently asked in competitive exams:
  • MRI (Magnetic Resonance Imaging) – Uses magnetic fields and radio waves.
  • PET Scan (Positron Emission Tomography) – Assesses metabolic activity of tissues.
  • Ultrasound (Sonography) – Uses high-frequency sound waves and involves no ionizing radiation.

Correct Answer: (D) It measures the heart beat.

Explanation

An Electrocardiogram (ECG or EKG) is a diagnostic test that records the electrical activity of the heart. It helps evaluate the heart rate and rhythm (heartbeat) and detect abnormalities such as arrhythmias, heart attacks (myocardial infarction), and conduction defects.

Exam Facts

• ECG (Electrocardiogram) records the electrical activity of the heart using electrodes placed on the skin.
• It helps diagnose:
  • Irregular heartbeat (Arrhythmia)
  • Heart attack (Myocardial Infarction)
  • Heart block and other conduction abnormalities
• The normal ECG waveform consists of:
  • P wave – Atrial depolarization.
  • QRS complex – Ventricular depolarization.
  • T wave – Ventricular repolarization.
• Related diagnostic tests:
  • EEG (Electroencephalogram) – Records the electrical activity of the brain.
  • EMG (Electromyography) – Measures the electrical activity of muscles.
  • Echocardiography (Echo) – Uses ultrasound to assess the heart’s structure and pumping function.
  • Doppler Ultrasound – Measures blood flow through blood vessels.

Correct Answer: (A) Mosquito

Explanation

Zika virus disease is primarily transmitted through the bite of an infected female Aedes mosquito, especially Aedes aegypti and Aedes albopictus. The virus can also spread through mother-to-child transmission during pregnancy, sexual contact, blood transfusion (rare), and organ transplantation.

Exam Facts

• Zika virus is mainly transmitted by Aedes aegypti and Aedes albopictus mosquitoes.
• The Aedes mosquito also transmits:
  • Dengue
  • Chikungunya
  • Yellow Fever
• Common symptoms of Zika virus infection include:
  • Mild fever
  • Skin rash
  • Joint pain
  • Red eyes (conjunctivitis)
  • Headache
• Zika infection during pregnancy can cause microcephaly and other congenital abnormalities in the baby (Congenital Zika Syndrome).
• Frequently asked disease–vector pairs:
  • Malaria → Female Anopheles mosquito
  • Dengue, Zika, Chikungunya, Yellow Fever → Aedes mosquito
  • Filariasis (Elephantiasis) → Culex mosquito
  • Kala-azar (Leishmaniasis) → Sandfly

Correct Answer: (C) 1967

Explanation

The first successful human heart transplant was performed on 3 December 1967 by Dr. Christiaan Barnard at Groote Schuur Hospital in Cape Town, South Africa. The recipient, Louis Washkansky, survived for 18 days after the operation before dying of pneumonia due to immunosuppression. The surgery marked a major milestone in the history of modern medicine.

Exam Facts

• First successful human heart transplant:
  • Date: 3 December 1967
  • Surgeon: Dr. Christiaan Barnard
  • Place: Groote Schuur Hospital, Cape Town, South Africa
• The first heart transplant in India was successfully performed by Dr. P. Venugopal at AIIMS, New Delhi, in 1994.
• The heart is a muscular organ with four chambers:
  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
• The first successful human kidney transplant was performed in 1954 by Dr. Joseph Murray, who later received the Nobel Prize in Physiology or Medicine (1990).
• The first test-tube baby (IVF) was Louise Brown, born in 1978 in the United Kingdom.

Correct Answer: (B) Acquired Immuno-Deficiency Syndrome

Explanation

AIDS stands for Acquired Immuno-Deficiency Syndrome. It is the advanced stage of infection caused by the Human Immunodeficiency Virus (HIV). HIV attacks the body’s CD4 (T-helper) lymphocytes, weakening the immune system and making the body vulnerable to opportunistic infections and certain cancers.

Exam Facts

• AIDS = Acquired Immuno-Deficiency Syndrome.
• HIV stands for Human Immunodeficiency Virus, the virus that causes AIDS.
• HIV primarily attacks CD4⁺ T-helper cells, reducing the body’s ability to fight infections.
• Common modes of HIV transmission:
  • Unprotected sexual contact
  • Transfusion of infected blood
  • Sharing contaminated needles or syringes
  • Mother-to-child transmission during pregnancy, childbirth, or breastfeeding
• HIV is not transmitted through:
  • Handshakes or hugging
  • Sharing food or utensils
  • Mosquito bites
  • Casual social contact
• World AIDS Day is observed every year on 1 December to raise awareness about HIV/AIDS.

Correct Answer: (A) Blood Sugar

Explanation

The Oral Glucose Tolerance Test (OGTT) is used to measure how well the body processes glucose (blood sugar). After an overnight fast, the person drinks a standard glucose solution, and blood glucose levels are measured at specific intervals (commonly after 2 hours). The test is used to diagnose diabetes mellitus, prediabetes, and gestational diabetes.

Exam Facts

• OGTT (Oral Glucose Tolerance Test) evaluates the body’s ability to metabolize glucose.
• It is commonly used to diagnose:
  • Diabetes Mellitus
  • Prediabetes (Impaired Glucose Tolerance)
  • Gestational Diabetes Mellitus (GDM) during pregnancy.
• The test involves:
  • Overnight fasting
  • Drinking a 75 g glucose solution (for adults)
  • Measuring blood glucose levels before and after glucose intake.
• Other important diabetes-related tests:
  • Fasting Blood Sugar (FBS) – Blood glucose after 8–12 hours of fasting.
  • Postprandial Blood Sugar (PPBS) – Blood glucose measured about 2 hours after a meal.
  • HbA1c (Glycated Hemoglobin) – Indicates the average blood glucose level over the previous 2–3 months.
• Insulin, secreted by the β-cells of the pancreas (Islets of Langerhans), helps regulate blood glucose levels.

Correct Answer: (A) Person having O group blood Explanation

In the ABO blood group system, people with blood group O are considered universal donors because their red blood cells do not have A or B antigens, reducing the risk of transfusion reactions. More precisely, O negative (O⁻) is the universal donor for red blood cell transfusions because it also lacks the Rh (D) antigen.

Exam Note: Since the options mention only the ABO blood groups, the correct answer is O group blood.

Exam Facts

• Universal donor (RBC transfusion): O⁻ (O negative).
• Universal recipient (RBC transfusion): AB⁺ (AB positive).
• Karl Landsteiner discovered the ABO blood group system in 1900 and received the Nobel Prize in Physiology or Medicine (1930).
• Blood group antigens:
  • A group → A antigen, anti-B antibodies.
  • B group → B antigen, anti-A antibodies.
  • AB group → A and B antigens, no anti-A or anti-B antibodies.
  • O group → No A or B antigens, both anti-A and anti-B antibodies.
• The Rh factor (D antigen) determines whether a blood group is positive (+) or negative (−). For safe transfusion, both ABO and Rh compatibility must be considered.

Correct Answer: (B) It is a wireless communication system that relies on LED/light signals.

Explanation

Li-Fi (Light Fidelity) is a wireless communication technology that uses LED (Light Emitting Diode) light to transmit data instead of radio waves. Data is transmitted by rapidly varying the intensity of LED light, a change that is too fast for the human eye to detect. Li-Fi can provide very high-speed internet connectivity in environments where radio-frequency communication is unsuitable.

Exam Facts

• Li-Fi stands for Light Fidelity.
• It uses visible light emitted by LED bulbs to transmit data wirelessly.
• Professor Harald Haas of the University of Edinburgh is widely regarded as the pioneer of Li-Fi technology and introduced the concept in 2011.
• Li-Fi vs Wi-Fi:
  • Li-Fi uses visible light for communication.
  • Wi-Fi uses radio waves.
• Advantages of Li-Fi:
  • Very high data transmission speed.
  • More secure, as light cannot pass through walls.
  • Reduced electromagnetic interference, making it suitable for hospitals, aircraft, and defence applications.
• Limitation:
  • Li-Fi generally requires a direct or reflected light path and does not work through opaque obstacles like walls.

Correct Answer: (A) Edwin Land

Explanation

The Polaroid instant camera was invented and developed by Dr. Edwin Herbert Land, the founder of the Polaroid Corporation. He introduced the first commercial instant camera, the Polaroid Model 95, in 1948. This revolutionary camera produced a fully developed photograph within minutes after taking the picture.

Exam Facts

• Edwin H. Land invented the Polaroid instant camera and founded the Polaroid Corporation.
• The first commercial Polaroid instant camera (Model 95) was launched in 1948.
• Edwin Land also invented the Polaroid polarizing filter, which is widely used in sunglasses, cameras, microscopes, and LCD displays.
• The instant camera works using self-developing photographic film, where the chemicals required for developing the image are contained within the film pack.
• Other notable inventions frequently asked in competitive exams:
  • Telephone – Alexander Graham Bell
  • Television – John Logie Baird
  • World Wide Web (WWW) – Tim Berners-Lee
  • Printing Press – Johannes Gutenberg
  • X-rays – Wilhelm Conrad Röntgen

Correct Answer: (C) Electromagnetic waves

Explanation

Light waves are electromagnetic waves that consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation. Unlike mechanical waves, they do not require a material medium and can travel through a vacuum at the speed of light.

Exam Facts

• Light is an electromagnetic wave and can travel through a vacuum.
• The speed of light in vacuum is 3 × 10⁸ m/s (approximately 300,000 km/s).
• Electromagnetic waves are transverse waves, not longitudinal waves.
• The electromagnetic spectrum (from longest to shortest wavelength):
  • Radio waves
  • Microwaves
  • Infrared rays
  • Visible light
  • Ultraviolet (UV) rays
  • X-rays
  • Gamma rays
• Examples of mechanical waves (which require a material medium):
  • Sound waves
  • Water waves
  • Seismic waves
• Visible light has a wavelength range of approximately 400–700 nm, with violet having the shortest wavelength and red the longest.

Correct Answer (Historically): Herbert Spencer (not listed among the options).

Exam Note: This question is incorrectly framed. The phrase “Survival of the fittest” was coined by Herbert Spencer in 1864 after reading Darwin’s theory of evolution. Charles Darwin later adopted this phrase in the 5th edition (1869) of On the Origin of Species.

Explanation

The phrase “Survival of the fittest” describes the principle that organisms best adapted to their environment are more likely to survive and reproduce. Although it is closely associated with Charles Darwin’s Theory of Natural Selection, the phrase itself was introduced by Herbert Spencer.

Exam Facts

• Herbert Spencer coined the term “Survival of the Fittest” in 1864.
• Charles Darwin proposed the Theory of Natural Selection and later adopted Spencer’s phrase.
• Natural selection is the process by which organisms with favourable heritable traits survive and reproduce more successfully.
• Jean-Baptiste Lamarck proposed the Theory of Inheritance of Acquired Characters.
• Gregor Mendel is known as the Father of Genetics for formulating the laws of inheritance.
• August Weismann proposed the Germ Plasm Theory, demonstrating that acquired characteristics are not inherited.

Correct Answer: (D) 573 K

Explanation

The absolute temperature is measured on the Kelvin (K) scale.

The conversion formula is:

K = °C + 273 (approximately 273.15)

So,

300°C + 273 = 573 K

Therefore, the correct answer is 573 K.

Exam Facts

• Conversion formulas:
  • Kelvin (K) = Celsius (°C) + 273
  • Celsius (°C) = Kelvin (K) − 273
• 0 K is called Absolute Zero, the lowest possible temperature.
• Absolute Zero = 0 K = −273.15°C.
• At 0°C, the absolute temperature is 273 K.
• At 100°C, the absolute temperature is 373 K.
• The SI unit of temperature is the Kelvin (K).
• Lord Kelvin (William Thomson) introduced the absolute temperature scale, also known as the Kelvin scale.

Correct Answer: (C) Hertz (Hz)

Explanation

Frequency is the number of oscillations, vibrations, or cycles completed per second. Its SI unit is the Hertz (Hz).

• 1 Hertz (Hz) = 1 cycle per second = 1 s⁻¹

Exam Facts

• SI unit of frequency: Hertz (Hz).
• Frequency (f) is the reciprocal of the time period (T):
  • f = 1/T
• SI unit of time period: Second (s).
• The unit Hertz (Hz) is named after the German physicist Heinrich Hertz, who experimentally confirmed the existence of electromagnetic waves.
• Common SI units asked in competitive exams:
  • Force – Newton (N)
  • Energy/Work – Joule (J)
  • Power – Watt (W)
  • Pressure – Pascal (Pa)
  • Electric Current – Ampere (A)
  • Electric Charge – Coulomb (C)
  • Potential Difference – Volt (V)
  • Resistance – Ohm (Ω)
  • Frequency – Hertz (Hz)

Correct Answer: (D) An iron compound

Explanation

Haemoglobin (Hemoglobin) is an iron-containing protein found in red blood cells (RBCs). It contains a heme group with a ferrous iron (Fe²⁺) ion, which binds oxygen in the lungs and transports it to different parts of the body. It also helps transport a small amount of carbon dioxide back to the lungs.

Exam Facts

• Haemoglobin is an iron-containing respiratory pigment present in red blood cells (RBCs).
• Each haemoglobin molecule contains 4 heme groups, each with one Fe²⁺ (ferrous) ion, allowing one molecule to carry 4 oxygen molecules (O₂).
• The normal haemoglobin level is approximately:
  • Men: 13.5–17.5 g/dL
  • Women: 12.0–15.5 g/dL
• Iron deficiency can lead to anaemia, causing symptoms such as fatigue, weakness, and shortness of breath.
• Other important biological pigments:
  • Chlorophyll contains Magnesium (Mg).
  • Vitamin B₁₂ (Cobalamin) contains Cobalt (Co).
  • Hemocyanin (found in some molluscs and arthropods) contains Copper (Cu) and carries oxygen.

Correct Answer: (C) Kepler Telescope

Explanation

The Kepler Space Telescope, launched by NASA in 2009, was designed to discover exoplanets (planets outside our Solar System). During its mission, Kepler discovered thousands of exoplanets and planetary candidates, including announcements of 26 newly confirmed planets in various studies. It revolutionized our understanding of planetary systems in the Milky Way.

Exam Facts

• Kepler Space Telescope was launched by NASA on 7 March 2009.
• It detects planets mainly using the transit method, observing the slight dimming of a star when a planet passes in front of it.
• Kepler has discovered and confirmed thousands of exoplanets, making it one of the most successful planet-hunting missions.
• The mission officially ended in 2018 after the spacecraft ran out of fuel.
• Other important space telescopes:
  • Hubble Space Telescope (1990) – Visible, ultraviolet, and near-infrared observations.
  • James Webb Space Telescope (JWST, 2021) – Infrared telescope for studying the early universe, galaxies, stars, and exoplanet atmospheres.
  • Chandra X-ray Observatory – Studies X-ray emissions from black holes, supernovae, and galaxy clusters.

Correct Answer: (A) Boiling point increases with increase in pressure

Explanation

A pressure cooker is a sealed vessel in which steam cannot escape easily. As water is heated, the pressure inside the cooker increases, causing the boiling point of water to rise above 100°C. Since the food cooks at a higher temperature, it cooks faster and retains more nutrients.

Exam Facts

• A pressure cooker works on the principle that the boiling point of a liquid increases with increasing pressure.
• At normal atmospheric pressure (1 atm), water boils at 100°C.
• Inside a pressure cooker, the boiling point of water rises to about 120°C, reducing cooking time.
• At high altitudes, atmospheric pressure is lower, so water boils below 100°C, making cooking slower.
• The safety valve on a pressure cooker releases excess steam if the internal pressure becomes too high, preventing accidents.

Correct Answer: (B) Mass

Explanation

A scalar quantity is a physical quantity that has only magnitude and no direction. Mass is a scalar quantity because it measures the amount of matter in an object and does not depend on direction.

On the other hand:

• Momentum has both magnitude and direction, so it is a vector.
• Weight is the gravitational force acting on a body, so it is a vector.
• Force also has magnitude and direction, making it a vector.

Exam Facts

Scalar Quantities (Magnitude only)

• Mass
• Time
• Distance
• Speed
• Energy
• Work
• Power
• Temperature
• Volume
• Density

Vector Quantities (Magnitude + Direction)

• Force
• Weight
• Velocity
• Acceleration
• Displacement
• Momentum
• Impulse
• Torque
• Mass remains constant everywhere.
• Weight = Mass × Acceleration due to gravity (W = mg), so weight changes with gravity (e.g., it is less on the Moon than on Earth).
• SI unit of Mass: kilogram (kg)
• SI unit of Force/Weight: newton (N)

Correct Answer: (A) Act as catalysts in life processes

Explanation

Enzymes are biological catalysts, mostly composed of proteins, that speed up biochemical reactions in living organisms without being consumed in the process. They lower the activation energy of chemical reactions, making essential life processes such as digestion, respiration, DNA replication, and metabolism occur rapidly and efficiently.

Exam Facts

• Enzymes are biological catalysts and are mostly proteins.
• They increase the rate of chemical reactions by lowering the activation energy.
• Enzymes are highly specific, with each enzyme acting on a particular substrate.
• Enzymes work best at an optimum temperature (around 37°C in humans) and an optimum pH.
• Common enzymes and their functions:
  • Amylase – Breaks down starch into sugars.
  • Pepsin – Digests proteins in the stomach.
  • Trypsin – Continues protein digestion in the small intestine.
  • Lipase – Breaks down fats into fatty acids and glycerol.
  • Catalase – Converts hydrogen peroxide (H₂O₂) into water and oxygen.
• Not all enzymes are proteins. Ribozymes are RNA molecules that also possess catalytic activity. However, for competitive examinations, enzymes are generally considered proteins.

Correct Answer: (C) AIDS

Explanation

AIDS (Acquired Immuno-Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV) and can be transmitted through infected blood, unprotected sexual contact, sharing contaminated needles, and mother-to-child transmission during pregnancy, childbirth, or breastfeeding.

Exam Facts

• AIDS is caused by the Human Immunodeficiency Virus (HIV).
• HIV is transmitted through:
  • Transfusion of infected blood
  • Unprotected sexual contact
  • Sharing contaminated needles or syringes
  • Mother-to-child transmission
• HIV is not transmitted by:
  • Handshakes or hugging
  • Sharing food or utensils
  • Mosquito bites
  • Casual social contact
• Other diseases in the options:
  • Cholera – Water-borne disease caused by Vibrio cholerae.
  • Tuberculosis (TB) – Air-borne disease caused by Mycobacterium tuberculosis.
  • Polio – Primarily spread through the faeco-oral route via contaminated food or water.
• World AIDS Day is observed every year on 1 December.

Correct Answer: (A) Sodium and potassium salts of higher fatty acids

Explanation

Soaps are the sodium or potassium salts of long-chain (higher) fatty acids such as stearic acid, palmitic acid, and oleic acid. They are produced by the saponification reaction, in which fats or oils react with sodium hydroxide (NaOH) or potassium hydroxide (KOH).

• Sodium soaps are hard soaps (e.g., bathing and laundry soaps).
• Potassium soaps are soft soaps (e.g., liquid soaps and shaving creams).

Exam Facts

• Soaps are sodium or potassium salts of higher fatty acids.
• Saponification is the reaction between fats/oils and alkalis (NaOH or KOH) to produce soap and glycerol.
• Hard water reduces the cleansing action of soap by forming an insoluble scum with calcium and magnesium ions.
• Synthetic detergents are generally sodium salts of sulphonic acids or alkyl benzene sulphonates, and unlike soaps, they work effectively in hard water.
• The cleansing action of soap is due to the formation of micelles, which trap grease and dirt, allowing them to be washed away with water.

Correct Answer: (C) Bauxite

Explanation

Bauxite is the chief ore of aluminium. It consists mainly of hydrated aluminium oxides along with impurities such as iron oxides, silica, and titanium dioxide. Aluminium is extracted from bauxite by first obtaining alumina (Al₂O₃) through the Bayer Process, followed by the Hall–Héroult electrolytic process.

Exam Facts

• Chief ore of Aluminium: Bauxite.
• Chemical composition of Bauxite: Mainly hydrated aluminium oxide (Al₂O₃·2H₂O, though composition varies).
• Extraction of Aluminium:
  • Bayer Process → Purification of bauxite to obtain Alumina (Al₂O₃).
  • Hall–Héroult Process → Electrolytic reduction of alumina to produce Aluminium metal.
• Other important ores:
  • Haematite (Fe₂O₃) → Ore of Iron.
  • Dolomite (CaMg(CO₃)₂) → Source of Calcium and Magnesium.
  • Carnallite (KCl·MgCl₂·6H₂O) → Ore of Magnesium and source of Potassium.
• Aluminium is:
  • Lightweight
  • Corrosion-resistant (due to a protective oxide layer)
  • Good conductor of electricity and heat
  • Widely used in aircraft, electrical transmission lines, packaging, and construction.

Correct Answer: (A) Vitamin A

Explanation

Night blindness (Nyctalopia) is caused by the deficiency of Vitamin A (Retinol). Vitamin A is essential for the formation of rhodopsin (visual purple), a pigment present in the rod cells of the retina that enables vision in dim light. A deficiency of Vitamin A impairs the production of rhodopsin, making it difficult to see in low-light conditions.

Exam Facts

• Vitamin A deficiency causes:
  • Night blindness (Nyctalopia)
  • Xerophthalmia (dryness of the eyes)
  • Bitot’s spots
  • In severe cases, corneal ulceration and blindness
• Rich sources of Vitamin A:
  • Carrot
  • Spinach and other green leafy vegetables
  • Mango
  • Papaya
  • Milk and butter
  • Egg yolk
  • Fish liver oil
• Important vitamin deficiency diseases:
  • Vitamin B₁ (Thiamine) → Beriberi
  • Vitamin B₃ (Niacin) → Pellagra
  • Vitamin C (Ascorbic Acid) → Scurvy
  • Vitamin D → Rickets (children), Osteomalacia (adults)
  • Vitamin K → Delayed blood clotting (excessive bleeding)
• Rod cells are responsible for vision in dim light, while cone cells are responsible for colour vision and sharp vision.

Correct Answer: (B) 2.50

Explanation

The molecular mass of chlorine gas (Cl₂) is approximately 70.9 g/mol, while the average molecular mass of air is about 29 g/mol.
$$\frac{70.9}{29} \approx 2.45 \approx 2.5$$

Therefore, chlorine gas is approximately 2.5 times heavier than air.

Exam Facts

• Chemical formula of chlorine gas: Cl₂
• Molecular mass of Cl₂: 70.9 g/mol
• Average molecular mass of air: ≈ 29 g/mol
• Since chlorine is heavier than air, it tends to accumulate in low-lying areas, making leaks particularly hazardous.
• Chlorine is a greenish-yellow gas with a pungent, irritating smell.
• It is widely used for:
  • Disinfection of drinking water and swimming pools
  • Manufacture of bleaching powder (CaOCl₂)
  • Production of PVC (Polyvinyl Chloride) and other chemicals
• Chlorine gas is highly toxic and can irritate the eyes, skin, and respiratory tract.

Explanation

When chlorine reacts with excess ammonia (NH₃), nitrogen gas (N₂) and ammonium chloride (NH₄Cl) are formed.

Balanced chemical equation:
$$\mathbf{8NH_3 + 3Cl_2 \rightarrow 6NH_4Cl + N_2}$$

The excess ammonia converts the chlorine into harmless products, producing white fumes of ammonium chloride.

Exam Facts

• Excess ammonia + chlorine → Nitrogen gas (N₂) + Ammonium chloride (NH₄Cl).
• Excess chlorine + ammonia → Nitrogen trichloride (NCl₃), an explosive yellow oily liquid.
• White fumes observed during the reaction are due to the formation of ammonium chloride (NH₄Cl).
• Ammonia (NH₃) is a colourless gas with a pungent smell and is highly soluble in water.
• Chlorine (Cl₂) is a greenish-yellow, toxic gas widely used in water purification, bleaching, and the manufacture of PVC.

Correct Answer: (C) Malaria

Explanation

Malaria is transmitted by the bite of an infected female Anopheles mosquito. The disease is caused by protozoan parasites of the genus Plasmodium, not by the mosquito itself. The mosquito acts as the vector, carrying the parasite from one person to another.

Exam Facts

• Disease: Malaria
• Causative organism: Plasmodium (Protozoa)
• Vector: Female Anopheles mosquito
• Major species causing malaria in humans:
  • Plasmodium falciparum (most severe)
  • Plasmodium vivax
  • Plasmodium malariae
  • Plasmodium ovale
  • Plasmodium knowlesi
• Common symptoms:
  • High fever with chills
  • Sweating
  • Headache
  • Fatigue
  • Anaemia (in severe cases)

Important Disease–Vector Pairs (Frequently Asked in Exams)

Correct Answer: (C) Pancreas

Explanation

Insulin is a hormone secreted by the β (beta) cells of the Islets of Langerhans in the pancreas. It regulates blood glucose (blood sugar) levels by helping body cells absorb glucose from the blood and by promoting the storage of excess glucose as glycogen in the liver and muscles.

Exam Facts

• Insulin is secreted by the β-cells of the Islets of Langerhans in the pancreas.
• Glucagon, another pancreatic hormone, is secreted by the α (alpha) cells and raises blood glucose levels.
• Insulin deficiency or resistance leads to Diabetes Mellitus.
• The pancreas is a mixed gland:
  • Endocrine function – Secretes hormones such as insulin and glucagon.
  • Exocrine function – Secretes digestive enzymes into the small intestine.
• Important endocrine glands and their hormones:
  • Pituitary gland – Growth Hormone (GH), TSH, ACTH, FSH, LH, Prolactin
  • Thyroid gland – Thyroxine (T₄), Triiodothyronine (T₃), Calcitonin
  • Adrenal gland – Adrenaline (Epinephrine), Cortisol, Aldosterone
  • Pancreas – Insulin and Glucagon

Correct Answer: (A) Only the upper surface of the leaf

Explanation

Lotus is a floating aquatic plant. Since the lower surface of the leaf remains in contact with water, stomata on that surface would not function effectively for gaseous exchange. Therefore, stomata are present only on the upper surface (upper epidermis), which is exposed to air.

Exam Facts

• Stomata are tiny pores in the epidermis of leaves that regulate:
  • Gaseous exchange (CO₂ and O₂)
  • Transpiration (loss of water vapour)
• Distribution of stomata in different plants:
  • Floating aquatic plants (e.g., Lotus, Water Lily): Stomata only on the upper surface.
  • Terrestrial dicot plants: Stomata are mostly on the lower surface.
  • Monocot plants (e.g., grasses): Stomata are present on both upper and lower surfaces.
  • Submerged aquatic plants (e.g., Hydrilla): No stomata; gaseous exchange occurs through the plant surface.
• Guard cells surround each stoma and control its opening and closing.
• Transpiration helps in:
  • Cooling the plant.
  • Transporting water and minerals from roots to leaves.
  • Maintaining the water balance of the plant.

Correct Answer: (C) γ-rays

Explanation

Gamma (γ) rays have the highest penetrating power among the three types of radioactive radiations. They are high-energy electromagnetic waves with no mass and no electric charge, allowing them to penetrate deeply through matter. Thick layers of lead or concrete are required to absorb or block gamma rays.

Exam Facts

• Order of Penetrating Power:
  γ > β > α
• Order of Ionizing Power:
  α > β > γ
• Alpha particles are the heaviest and most ionizing, but they travel only a short distance.
• Beta particles have greater penetrating power than alpha particles but less than gamma rays.
• Gamma rays are used in:
  • Cancer radiotherapy
  • Sterilization of medical equipment
  • Industrial radiography
  • Food irradiation

Explanation

A kilowatt-hour (kWh) is a unit of energy, not power. It represents the amount of energy consumed when a 1 kilowatt (1000 W) electrical appliance operates for 1 hour.

Calculation:

• 1 kWh = 1000 W × 3600 s
• 1 kWh = 3.6 × 10⁶ joules (J)

This is the standard unit used by electricity supply companies to measure electrical energy consumption.

Exam Facts

• SI unit of Energy: Joule (J)
• Commercial unit of electrical energy: Kilowatt-hour (kWh)
• 1 kWh = 1000 Wh = 3.6 × 10⁶ J
• SI unit of Power: Watt (W)
• 1 kilowatt (kW) = 1000 watts (W)
• Power is the rate of doing work or consuming energy.
• Energy = Power × Time
• Electricity bills are based on the number of units consumed, where:
  • 1 Unit of Electricity = 1 kWh
• Common SI units asked in exams:
  • Energy → Joule (J)
  • Power → Watt (W)
  • Force → Newton (N)
  • Momentum → kg·m/s
  • Pressure → Pascal (Pa)

Correct Answer: (A) N₂, CO and (C) CO, CN⁻

Note: As written, the question has two correct answers. Both (A) and (C) are isoelectronic because they contain the same total number of electrons (14).

Explanation

Isoelectronic species are atoms, ions, or molecules having the same number of electrons and often a similar electronic configuration.

Correct Answer: (C) Loss or gain of electron

Explanation

Ions are electrically charged atoms or groups of atoms formed when a neutral atom loses or gains electrons.

• Loss of electrons → Positive ion (Cation)
• Gain of electrons → Negative ion (Anion)

The number of protons remains unchanged during ion formation; only the number of electrons changes.

Exam Facts

• Cation (+): Formed by loss of electrons.
  • Example:
    • Na → Na⁺ + e⁻
    • Mg → Mg²⁺ + 2e⁻
• Anion (−): Formed by gain of electrons.
  • Example:
    • Cl + e⁻ → Cl⁻
    • O + 2e⁻ → O²⁻
• Sharing of electrons leads to the formation of covalent bonds, not ions.
  • Example:
    • H₂, O₂, CH₄, H₂O
• Transfer of electrons leads to the formation of ionic bonds.
  • Example:
    • NaCl, MgO, CaCl₂
• Important distinction:
  • Ionic compounds are formed by electron transfer.
  • Covalent compounds are formed by electron sharing.

Correct Answer: (C) Ammeter

Explanation

An ammeter is an instrument used to measure electric current in an electrical circuit. It is connected in series with the circuit so that the same current passes through both the circuit and the ammeter. An ideal ammeter has very low (ideally zero) resistance to avoid affecting the current being measured.

Exam Facts

• Ammeter measures electric current.
• SI unit of electric current: Ampere (A).
• Ammeter is connected in series and has very low resistance.
• Other electrical measuring instruments:
  • Voltmeter → Measures potential difference (voltage); connected in parallel and has very high resistance.
  • Galvanometer → Detects and measures very small electric currents.
  • Potentiometer → Measures or compares electromotive force (EMF) and potential difference accurately without drawing current from the source.
• Important SI units:
  • Current → Ampere (A)
  • Voltage → Volt (V)
  • Resistance → Ohm (Ω)
  • Power → Watt (W)
  • Charge → Coulomb (C)

Correct Answer: (A) Mg, Ca

Explanation

Magnesium (Mg) and Calcium (Ca) both belong to Group 2 of the Modern Periodic Table, known as the Alkaline Earth Metals. Elements in the same group have the same number of valence electrons and therefore exhibit similar chemical properties.

Exam Facts

• Magnesium (Mg):
  • Atomic Number: 12
  • Group: 2
  • Period: 3
• Calcium (Ca):
  • Atomic Number: 20
  • Group: 2
  • Period: 4
• Group 2 (Alkaline Earth Metals):
  • Beryllium (Be)
  • Magnesium (Mg)
  • Calcium (Ca)
  • Strontium (Sr)
  • Barium (Ba)
  • Radium (Ra)

Other Elements in the Options

• Potassium (K) → Group 1 (Alkali Metals)
• Copper (Cu) → Group 11 (Transition Metal)
• Iodine (I) → Group 17 (Halogen)

Important Periodic Table Groups

• Group 1: Alkali Metals (Li, Na, K, Rb, Cs, Fr)
• Group 2: Alkaline Earth Metals (Be, Mg, Ca, Sr, Ba, Ra)
• Group 17: Halogens (F, Cl, Br, I, At)
• Group 18: Noble Gases (He, Ne, Ar, Kr, Xe, Rn)

Exam Tip:
Elements in the same group have the same number of valence electrons and show similar chemical properties, while elements in the same period have the same number of electron shells.

Correct Answer: (B) Watt

Explanation

Power is the rate at which work is done or energy is transferred. The SI unit of power is the Watt (W).

• 1 Watt = 1 Joule per second (1 W = 1 J/s)

This means a device has a power of 1 watt if it uses or transfers 1 joule of energy every second.

Exam Facts

• SI unit of Power: Watt (W)
• Named after: James Watt, the Scottish engineer.
• Formula for Power:
  • Power = Work / Time (P = W/t)
  • Electrical Power = Voltage × Current (P = VI)
• SI unit of Work/Energy: Joule (J)
• SI unit of Voltage: Volt (V)
• 1 Horsepower (hp) ≈ 746 W
• Commercial unit of electrical energy:Kilowatt-hour (kWh)
  • 1 kWh = 3.6 × 10⁶ J

Important SI Units for Competitive Exams

Correct Answer: (C) γ-rays

Explanation

Gamma (γ) rays are the most harmful among the given options because they have the highest penetrating power. They can pass through human tissues and damage cells, DNA, and internal organs. High doses of gamma radiation can cause radiation sickness, cancer, and genetic mutations.

Exam Facts

• Gamma (γ) rays are:
  • Electromagnetic radiation
  • No mass
  • No electric charge
  • Highest penetrating power
• Order of Penetrating Power:
  • γ > β > α
• Order of Ionizing Power:
  • α > β > γ
• Stopping materials:
  • α-particles → Stopped by paper or human skin.
  • β-particles → Stopped by aluminium sheets.
  • γ-rays → Require thick lead or concrete shielding.
• Applications of gamma rays:
  • Cancer treatment (radiotherapy)
  • Sterilization of medical instruments
  • Food irradiation
  • Industrial radiography

Correct Answer: (A) Neutrons in the nucleus

Explanation

Isotopes are atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons. Because the number of neutrons differs, isotopes have different mass numbers, although their chemical properties remain nearly identical.

Exam Facts

• Isotopes:
  • Same atomic number (same number of protons)
  • Different mass numbers (different number of neutrons)
• Atomic Number (Z) = Number of protons
• Mass Number (A) = Protons + Neutrons
• In a neutral atom:
  • Number of electrons = Number of protons
• Protons determine the identity of an element.
• Neutrons affect the mass and stability of the nucleus.

Common Examples of Isotopes

• Hydrogen
  • Protium (¹H): 1 proton, 0 neutrons
  • Deuterium (²H): 1 proton, 1 neutron
  • Tritium (³H): 1 proton, 2 neutrons
• Carbon
  • ¹²C, ¹³C, ¹⁴C
• Chlorine
  • ³⁵Cl and ³⁷Cl

Correct Answer: (D) F, Si, I

Explanation

In options (A), (B), and (C), all the elements belong to the same group of the Periodic Table:

• Cu, Ag, Au → Group 11 (Coinage metals)
• Na, K, Rb → Group 1 (Alkali metals)
• Zn, Cd, Hg → Group 12

However, in (D):

• F (Fluorine) → Group 17 (Halogen)
• Si (Silicon) → Group 14 (Carbon family)
• I (Iodine) → Group 17 (Halogen)

Since Silicon (Si) does not belong to the same group as Fluorine (F) and Iodine (I), this is the odd combination.

Exam Facts

• Group 1 (Alkali Metals): Li, Na, K, Rb, Cs, Fr
• Group 11 (Coinage Metals): Cu, Ag, Au
• Group 12: Zn, Cd, Hg
• Group 14 (Carbon Family): C, Si, Ge, Sn, Pb
• Group 17 (Halogens): F, Cl, Br, I, At, Ts
• Group 18 (Noble Gases): He, Ne, Ar, Kr, Xe, Rn

Important Point

• Elements in the same group have the same number of valence electrons and generally exhibit similar chemical properties.
• Elements in the same period have the same number of electron shells but different chemical properties.

Correct Answer: (A) They are much less reactive

Explanation

Saturated hydrocarbons (alkanes) are called paraffins because they are chemically less reactive. The word “paraffin” comes from the Latin words parum (little) and affinis (affinity), meaning “little affinity” or “low reactivity.”

Alkanes contain only single covalent bonds (C–C and C–H), which are strong and stable. Therefore, they do not readily undergo chemical reactions under normal conditions.

Exam Facts

• Paraffins = Alkanes = Saturated hydrocarbons.
• General formula of alkanes: CₙH₂ₙ₊₂
• They contain only single covalent bonds.
• They mainly undergo:
  • Combustion
  • Substitution reactions (especially with halogens in the presence of sunlight or UV light)
• Examples:
  • Methane (CH₄)
  • Ethane (C₂H₆)
  • Propane (C₃H₈)
  • Butane (C₄H₁₀)

Comparison of Hydrocarbons

Correct Answer: (B) cm³

Explanation

The CGS system stands for Centimetre–Gram–Second system of units.

Since volume = length³, and the unit of length in the CGS system is centimetre (cm), the unit of volume is:

Volume = cm × cm × cm = cm³

Therefore, the correct answer is cm³.

Exam Facts

CGS System

• Length: centimetre (cm)
• Mass: gram (g)
• Time: second (s)
• Volume: cm³
• Force: dyne
• Work/Energy: erg
• Pressure: barye (dyne/cm²)

SI (MKS) System

• Length: metre (m)
• Mass: kilogram (kg)
• Time: second (s)
• Volume: m³
• Force: newton (N)
• Work/Energy: joule (J)
• Pressure: pascal (Pa)

Important Conversions

• 1 m = 100 cm
• 1 m³ = (100 cm)³ = 10⁶ cm³
• 1 litre = 1000 cm³ = 1000 mL
• 1 cm³ = 1 mL

Correct Answer (based on the given options): (C) H₂SeO₄ (Selenic acid)

Note: In most competitive examinations, the question is usually asked as “Which acid (or acid mixture) dissolves gold?” The standard answer is Aqua Regia, not any single common acid.

Explanation

• Gold (Au) is a highly unreactive (noble) metal and does not dissolve in:
  • Nitric acid (HNO₃)
  • Sulphuric acid (H₂SO₄)
  • Perchloric acid (HClO₄) under ordinary conditions.
• Hot concentrated selenic acid (H₂SeO₄) is a powerful oxidizing acid and can dissolve gold, making (C) the correct answer among the given options.

Exam Facts

• Aqua Regia is the most common reagent used to dissolve gold.
• Composition of Aqua Regia:
  • 1 part concentrated HNO₃
  • 3 parts concentrated HCl
• It is called “Royal Water” because it can dissolve noble metals such as:
  • Gold (Au)
  • Platinum (Pt)
• Nitric acid alone dissolves silver (Ag) and copper (Cu) but not gold.
• Hydrochloric acid alone also does not dissolve gold.

Correct Answer: (C) Monocot flowers possess no nectaries.

Correct Answer: (B) West to East

Explanation

Geostationary satellites orbit the Earth from west to east, in the same direction as the Earth’s rotation. They orbit in the equatorial plane and take approximately 24 hours to complete one revolution, making them appear stationary over a fixed point on the Earth’s surface.

Exam Facts

• Geostationary satellites move from west to east, following the direction of Earth’s rotation.
• They orbit in the equatorial plane, at an altitude of approximately 35,786 km above the Earth’s surface.
• Their orbital period is approximately 24 hours (more precisely, one sidereal day: about 23 hours 56 minutes).
• A geostationary satellite appears stationary over the same point on the Earth’s equator.
• Geostationary satellites are particularly useful for weather forecasting, communication, television broadcasting and telecommunications.
• A geostationary orbit is possible only when the satellite has zero inclination and moves in a circular orbit in the direction of Earth’s rotation.
• The term geosynchronous is broader: a geosynchronous satellite has an orbital period equal to Earth’s rotation, while a geostationary satellite must additionally remain fixed over the equator.
• Polar satellites generally travel in near-polar orbits and are different from geostationary satellites.
• The Earth rotates from west to east, which is why a geostationary satellite must also orbit west to east to remain apparently fixed.

Correct Answer: (B) More than 1000 Hz

Explanation

When the source of sound (the train) approaches a stationary listener, the sound waves reach the listener more frequently because the source moves toward the listener. Therefore, the apparent frequency increases.

This phenomenon is known as the Doppler effect.

Exam Facts

• When a sound source approaches a stationary observer, the apparent frequency increases.
• When a sound source moves away from a stationary observer, the apparent frequency decreases.
• This change in observed frequency is called the Doppler effect.
• For a source approaching a stationary observer:
  Apparent frequency > Actual frequency.
• For a source receding from a stationary observer:
  Apparent frequency < Actual frequency.
• The Doppler effect applies to sound, light and other waves.
• The actual frequency of the whistle remains 1000 Hz; it is only the frequency perceived by the listener that changes.
• Common examples include the changing pitch of a train horn, ambulance siren or police siren as it approaches and then moves away.
• The Doppler effect is used in applications such as radar, astronomy, medical Doppler ultrasound and weather monitoring.

Correct Answer: (D) Constant

Explanation

The question states:

Displacement ∝ time²

Therefore:

s = k × t²

where k is a constant.

The equation of motion for uniformly accelerated motion is:

s = ut + (1/2) × a × t²

Since the displacement contains only a t² term, the acceleration a remains constant.

Hence, the body has constant acceleration.

Exam Facts

• If s ∝ t², the body is undergoing uniformly accelerated motion.
• In uniformly accelerated motion, acceleration remains constant.
• The standard equation of motion is s = ut + (1/2) × a × t².
• If a body starts from rest, then u = 0, so s = (1/2) × a × t².
• If s ∝ t, the body has constant velocity and acceleration is zero.
• In uniformly accelerated motion, velocity changes by equal amounts in equal intervals of time.
• The slope of a velocity-time graph gives acceleration.
• The area under a velocity-time graph gives displacement.

Correct Answer: (B) Relatively less at the front surface

Explanation

When a closed vessel containing gas accelerates horizontally, the gas develops a pressure gradient opposite to the direction of acceleration.

If the vessel accelerates forward, the gas tends to lag behind due to inertia. Consequently, pressure becomes higher at the back and lower at the front of the vessel.

Therefore, the pressure is relatively less at the front surface.

Exam Facts

• In an accelerating gas, pressure is not uniform throughout the vessel.
• If the vessel accelerates forward, pressure is higher at the back and lower at the front.
• The pressure gradient in the gas acts opposite to the direction of acceleration.
• This phenomenon is analogous to the pressure variation in a liquid inside an accelerating container.
• The pressure difference arises because of the inertial effect of the gas.
• If the vessel accelerates toward the right, the pressure is greater on the left/back side and smaller on the right/front side.
• The question specifically says to neglect gravity, so there is no vertical pressure gradient due to gravitational effects.
• If the vessel were not accelerating and gravity were also neglected, the gas pressure would be essentially uniform throughout the vessel.
• This principle is related to the concept of pseudo-force in a non-inertial frame of reference.

Correct Answer: (B) Positively charged

Explanation

A positively charged glass rod will repel another positively charged body because like charges repel. However, the question states that the rod first attracts and then repels the suspended body.

This can happen when the suspended body is initially negatively charged? A positive rod would attract it, but after contact, the negative charge can be neutralized or reversed, causing repulsion. However, in the standard electrostatics interpretation of “attracts and then repels” after contact, the body becomes positively charged after coming into contact with the positive rod.

Thus, the suspended body is positively charged.

Exam Facts

• Like charges repel each other.
• Unlike charges attract each other.
• A positively charged body can attract a neutral body due to electrostatic induction.
• If a neutral body touches a positively charged rod, electrons move toward the rod, leaving the body positively charged.
• After acquiring the same type of charge, the body is repelled by the positively charged rod.
• Therefore, attraction followed by repulsion after contact is an important indication that the suspended body has acquired the same charge as the rod.
• A negatively charged body would normally be attracted by a positively charged rod and would not ordinarily become positively charged merely through electrostatic induction without charge transfer.
• Electrostatic induction can cause attraction between a charged body and an initially neutral conductor without physical contact.
• A glass rod rubbed with silk generally becomes positively charged because it loses electrons.

Correct Answer: (A) North to South

Explanation

According to Oersted’s experiment, an electric current flowing through a conductor produces a magnetic field around the conductor.

Here, the wire is kept above the magnetic needle. For the N-pole to deflect towards the East, the magnetic field at the position of the needle must be directed towards the East.

Applying the Right-Hand Thumb Rule:

• Point the right thumb in the direction of current.
• The curled fingers indicate the direction of the magnetic field around the wire.
• When the current flows from North to South, the magnetic field at the point directly below the wire is directed towards the East.

Therefore, the current must flow North → South.

Exam Facts

• A current-carrying conductor produces a magnetic field around it.
• The direction of the magnetic field can be determined using the Right-Hand Thumb Rule.
• In this rule, the thumb points in the direction of conventional current, while the curled fingers indicate the direction of magnetic field.
• Oersted’s experiment demonstrated the magnetic effect of electric current.
• A freely suspended magnetic needle normally aligns itself approximately along the North-South direction because of Earth’s magnetic field.
• A current-carrying wire placed near a magnetic compass can cause the needle to deflect.
• If the direction of current is reversed, the direction of the magnetic field also reverses, and the needle deflects in the opposite direction.
• The magnetic field around a long straight current-carrying conductor consists of concentric circles centred on the conductor.
• The conventional current is considered to flow from positive to negative potential externally; electron flow is in the opposite direction.

Correct Answer: (C) Equal at all points

Explanation

For a body projected vertically upward, kinetic energy decreases as the body rises, while potential energy increases. At the highest point, the velocity becomes zero, so kinetic energy is minimum (zero), while potential energy is maximum.

However, according to the law of conservation of mechanical energy, the sum of kinetic energy and potential energy remains constant, provided air resistance is neglected.

Therefore, the total mechanical energy is equal at all points of the body’s motion.

Exam Facts

• Mechanical energy = Kinetic Energy + Potential Energy.
• In the absence of air resistance, the total mechanical energy of a vertically projected body remains constant.
• At the point of projection, kinetic energy is maximum and potential energy is minimum relative to the subsequent height.
• At the highest point, velocity becomes zero, so kinetic energy = 0.
• At the highest point, potential energy is maximum.
• During upward motion, kinetic energy decreases while potential energy increases.
• During downward motion, potential energy decreases while kinetic energy increases.
• The conversion between kinetic and potential energy does not change the total mechanical energy.
• If air resistance is considered, mechanical energy is not conserved because some energy is dissipated as heat and sound.
• The principle involved is the law of conservation of energy.

Correct Answer:

• (i) Urea → (iv) Fertilizer
• (ii) Chloroform → (iii) Anesthetic
• (iii) Phenol → (ii) Antiseptic
• (iv) Ethylene → (i) Fruit ripening

Explanation

Urea is a nitrogen-rich compound widely used as a fertilizer. Chloroform was historically used as an anesthetic. Phenol was one of the earliest chemicals widely used as an antiseptic/disinfectant. Ethylene is a plant hormone that promotes fruit ripening.

Therefore, the correct matching is:

(i)–(iv), (ii)–(iii), (iii)–(ii), (iv)–(i).

Exam Facts

• Urea (CO(NH₂)₂) is an important nitrogenous fertilizer containing about 46% nitrogen by mass.
• Urea is one of the most widely used nitrogen fertilizers in agriculture.
• Chloroform (CHCl₃) was historically used as a general anesthetic, although it is no longer routinely used for this purpose because of its toxicity.
• Phenol (C₆H₅OH) was historically used as an antiseptic and disinfectant.
• Joseph Lister pioneered the use of phenol (carbolic acid) in antiseptic surgery in the 19th century.
• Ethylene (C₂H₄) is a gaseous plant hormone involved in fruit ripening.
• Ethylene also promotes leaf and fruit abscission and contributes to senescence in plants.
• Ethylene is particularly associated with the ripening of climacteric fruits such as banana, mango and tomato.
• Urea → Fertilizer, Chloroform → Anesthetic, Phenol → Antiseptic, Ethylene → Fruit ripening is a useful direct match for competitive examinations.

Correct Answer: (D) Acidic or Neutral

Explanation

Phenolphthalein is an acid-base indicator that is colorless in acidic and neutral solutions but turns pink in alkaline (basic) solutions.

Therefore, if adding phenolphthalein produces no color change, the liquid could be either acidic or neutral. The absence of a pink color does not allow us to distinguish between these two.

Exam Facts

• Phenolphthalein is an acid-base indicator.
• Phenolphthalein is colorless in acidic and neutral solutions.
• Phenolphthalein turns pink to reddish-pink in alkaline solutions.
• Its approximate transition range is pH 8.2–10.0.
• Therefore, a colorless phenolphthalein solution does not necessarily mean the solution is neutral.
• Litmus can be used to distinguish acidic and basic solutions: blue litmus turns red in acid, while red litmus turns blue in base.
• Methyl orange is red in acidic medium and yellow in alkaline medium.
• A neutral solution at 25°C has a pH of approximately 7.
• Common alkaline substances include sodium hydroxide (NaOH) and potassium hydroxide (KOH).
• The key exam point is: Phenolphthalein: Acid/Neutral → Colourless; Base → Pink.

Correct Answer: (D) Noble/Inert gases

Explanation

The elements of Group 0 (modern Group 18) are known as noble gases or inert gases. They have a completely filled outermost electron shell, making them highly stable and generally unreactive.

The group includes Helium, Neon, Argon, Krypton, Xenon, Radon and Oganesson.

Exam Facts

• Group 0 in the older classification corresponds to Group 18 in the modern IUPAC numbering.
• Group 18 elements are called noble gases or inert gases.
• The noble gases are He, Ne, Ar, Kr, Xe, Rn and Og.
• Helium has 2 electrons in its outermost shell, while the other commonly occurring noble gases generally have 8 valence electrons.
• Noble gases have very low chemical reactivity because of their stable electronic configuration.
• Radon (Rn) is a radioactive noble gas.
• Oganesson (Og) is the heaviest known element in Group 18 and is synthetic and highly radioactive.
• Alkali metals belong to Group 1.
• Halogens belong to Group 17.
• Chalcogens belong to Group 16.
• The name “noble gases” is preferred over “inert gases” because some heavier noble gases, particularly xenon, can form chemical compounds under suitable conditions.

Correct Answer: (C) AlPO₄

Explanation

Aluminium forms the Al³⁺ ion, while phosphate is the PO₄³⁻ ion. Since their charges are equal and opposite, they combine in a 1:1 ratio to form a neutral compound:

Al³⁺ + PO₄³⁻ → AlPO₄

Therefore, the chemical formula of aluminium phosphate is AlPO₄.

Exam Facts

• Aluminium ion: Al³⁺
• Phosphate ion: PO₄³⁻
• Aluminium phosphate formula: AlPO₄.
• Aluminium phosphate is an ionic compound.
• The oxidation state of aluminium in AlPO₄ is +3.
• The phosphate ion has a charge of −3.
• The charges balance in a 1:1 ratio, giving AlPO₄.
• Al₂(PO₄)₃ is incorrect because the total charges would not balance: 2 × (+3) ≠ 3 × (−3).
• The common formula of aluminium oxide is Al₂O₃.
• The common formula of aluminium sulphate is Al₂(SO₄)₃.
• A useful rule for writing ionic formulas is to ensure that the total positive and negative charges are equal.

Correct Answer: (C) Soda lime / Quicklime

Explanation

Ammonia (NH₃) can be dried using quicklime (CaO) because quicklime absorbs water without reacting with ammonia.

Concentrated H₂SO₄ and phosphorus pentoxide (P₂O₅) cannot be used because they react with ammonia. Fused CaCl₂ is also unsuitable because it can absorb ammonia.

Therefore, soda lime or, more commonly, quicklime (CaO) is used for drying ammonia gas.

Exam Facts

• Quicklime (CaO) is commonly used to dry ammonia (NH₃).
• Quicklime removes moisture from ammonia without consuming the ammonia gas.
• Concentrated H₂SO₄ cannot dry ammonia because it reacts with NH₃ to form ammonium sulphate/bisulphate.
• P₂O₅ (phosphorus pentoxide) is a powerful dehydrating agent but reacts with ammonia, so it cannot be used to dry NH₃.
• Anhydrous CaCl₂ is generally unsuitable for drying ammonia because it absorbs ammonia and forms an addition compound.
• Soda lime is a mixture mainly containing NaOH and CaO and is also used as a drying agent for ammonia in some contexts.
• A common laboratory method for preparing dry ammonia is to pass NH₃ through a quicklime (CaO) drying tower.
• CaO + H₂O → Ca(OH)₂, which accounts for the removal of moisture.
• Important exam rule: The drying agent must remove water without reacting with or absorbing the gas being dried.

Correct Answer: (A) NO

Explanation

Copper reacts differently with dilute and concentrated nitric acid.

With dilute/moderately concentrated HNO₃, copper reduces nitric acid mainly to nitric oxide (NO): 3Cu+8HNO3​→3Cu(NO3​)2​+2NO+4H2​O

With concentrated HNO₃, the reduction product is mainly nitrogen dioxide (NO₂): Cu+4HNO3​→Cu(NO3​)2​+2NO2​+2H2​O

Thus, for moderately concentrated (1:1) nitric acid, the expected reduction product is NO.

Exam Facts

• Copper + dilute/moderately concentrated HNO₃ → NO.
• Copper + concentrated HNO₃ → NO₂.
• NO (nitric oxide) is a colourless gas when freshly formed.
• NO rapidly reacts with oxygen in air to form NO₂, which is a reddish-brown gas: 2NO+O2​→2NO2​
• NO₂ is a brown/reddish-brown, toxic gas with a pungent odour.
• Nitric acid acts as a strong oxidising agent in its reaction with copper.
• Copper does not liberate hydrogen gas with nitric acid because HNO₃ oxidises the hydrogen that would otherwise be produced.
• The copper is oxidised from Cu⁰ to Cu²⁺, forming copper(II) nitrate, Cu(NO₃)₂.
• Dilute HNO₃ → generally NO, while concentrated HNO₃ → generally NO₂ is an important reaction-based fact for competitive examinations.

Correct Answer: (B) Heating a platinum wire in a Bunsen burner

Explanation

When a platinum wire is heated in a Bunsen burner, it becomes red-hot due to the increase in temperature, but no new substance is formed. On cooling, it returns to its original state. Therefore, this is a physical change.

Magnesium and copper undergo chemical reactions when heated strongly in air, while quicklime reacts chemically with water.

Exam Facts

• A physical change does not result in the formation of a new substance.
• A chemical change results in the formation of one or more new substances.
• Platinum is a highly unreactive metal and does not readily react with oxygen on heating; therefore, heating a platinum wire is essentially a physical change.
• Magnesium burns in oxygen to form magnesium oxide (MgO): 2Mg+O2​→2MgO
• Magnesium burns with a bright white flame.
• Copper reacts with oxygen on strong heating and forms copper(II) oxide (CuO), producing a black coating: 2Cu+O2​→2CuO
• Quicklime (CaO) reacts vigorously with water to form slaked lime [Ca(OH)₂]: CaO+H2​O→Ca(OH)2​
• The reaction of quicklime with water is exothermic, meaning it releases heat.
• Change of state, shape, size or temperature without formation of a new substance is generally classified as a physical change.

Correct Answer: (D) Tall : Dwarf, 2 : 2

Explanation

Tallness (T) is dominant over dwarfness (t).

The cross is:

Tt × tt

Gametes produced:

• Tt → T, t
• tt → t, t

The offspring are:

• Tt → Tall
• Tt → Tall
• tt → Dwarf
• tt → Dwarf

Thus, there are 2 tall and 2 dwarf plants, giving a phenotypic ratio of:

Tall : Dwarf = 2 : 2 = 1 : 1

Therefore, Option (D) is correct.

Exam Facts

• In pea plants, T represents the dominant allele for tallness.
• t represents the recessive allele for dwarfness.
• Tt is a heterozygous (hybrid) tall plant.
• tt is a homozygous recessive dwarf plant.
• The cross Tt × tt is called a test cross.
• The phenotypic ratio in a typical monohybrid test cross is 1 tall : 1 dwarf.
• The genotypic ratio is also 1 Tt : 1 tt.
• Tt → Tall because the dominant allele T masks the recessive t allele.
• tt → Dwarf because no dominant T allele is present.
• The classic 3 : 1 phenotypic ratio occurs in the F₂ generation of a monohybrid cross between two heterozygotes: Tt × Tt.
• Gregor Mendel conducted his famous inheritance experiments using the garden pea (Pisum sativum).

Correct Answer: (C) Both plant and bacterial cells

Explanation

A cell wall is a rigid, protective layer located outside the plasma membrane. It is present in plant cells and bacterial cells, but not in animal cells.

In plants, the cell wall is mainly composed of cellulose, while in most bacteria it is mainly composed of peptidoglycan (murein).

Therefore, the correct answer is (C) Both plant and bacterial cells.

Exam Facts

• Plant cells have a cell wall mainly made of cellulose.
• Bacterial cells generally have a cell wall made of peptidoglycan.
• Animal cells do not have a cell wall; they have only a plasma membrane surrounding the cell.
• The plant cell wall provides shape, mechanical strength and protection.
• The middle lamella of plant cells is mainly composed of pectin and helps bind adjacent plant cells.
• Bacterial cell walls help maintain cell shape and protect against osmotic pressure.
• Gram-positive bacteria have a relatively thick peptidoglycan layer.
• Gram-negative bacteria have a thinner peptidoglycan layer and an additional outer membrane.
• Fungi also have cell walls, but their walls are mainly composed of chitin, not cellulose.
• Cellulose is characteristic of plant cell walls, whereas chitin is characteristic of fungal cell walls.

Correct Answer: (B) Detritus consumers (Detritivores)

Explanation

A detritus food chain begins with dead organic matter (detritus) such as fallen leaves, dead plants and animal remains. Organisms such as insects, larvae, earthworms and nematodes feed on this dead organic material and break it into smaller particles.

These organisms are called detritivores or detritus consumers.

Exam Facts

• A detritus food chain starts with dead organic matter, rather than living green plants.
• Detritivores feed directly on dead and decaying organic matter.
• Examples of detritivores include earthworms, termites, millipedes, larvae and some insects.
• Nematodes are microscopic roundworms; many species participate in the decomposition and detrital food web.
• Decomposers such as bacteria and fungi chemically break down organic matter and release nutrients.
• Detritivores generally fragment and consume detritus, while decomposers carry out much of the microbial decomposition.
• A grazing food chain begins with living green plants (producers), whereas a detritus food chain begins with dead organic matter.
• Detritus food chains play an important role in nutrient recycling within ecosystems.
• Producers prepare their own food through processes such as photosynthesis.
• Secondary and tertiary consumers obtain energy by feeding on other consumers, rather than directly feeding on detritus.

Correct Answer: (B) Lamarck

Explanation

The concept of “Inheritance of acquired characters” was proposed by Jean-Baptiste Lamarck as part of his theory of evolution. Lamarck suggested that organisms acquire characteristics during their lifetime in response to their environment and that these acquired characteristics could be passed on to their offspring.

His theory is commonly associated with the principles of use and disuse of organs and the inheritance of acquired characters.

Exam Facts

• Jean-Baptiste Lamarck (1744–1829) proposed the theory of inheritance of acquired characters.
• Lamarck’s evolutionary theory is known as Lamarckism.
• Lamarck proposed the law of use and disuse: frequently used organs become stronger/developed, while unused organs tend to degenerate.
• The classic example associated with Lamarckism is the elongation of the giraffe’s neck due to repeated stretching to reach high leaves.
• Charles Darwin proposed the theory of evolution by natural selection.
• Alfred Russel Wallace independently developed the idea of natural selection around the same period as Darwin.
• Gregor Mendel established the basic laws of heredity through experiments on pea plants.
• Modern evolutionary biology does not accept Lamarck’s general claim that traits acquired during an individual’s lifetime are routinely inherited by offspring.
• Natural selection acts on heritable variations and is central to the modern understanding of Darwinian evolution.

Correct Answer: (B) Mangrove plants

Explanation

Pneumatophores are specialized aerial roots found in many mangrove plants growing in waterlogged and oxygen-deficient soils. These roots generally grow upward above the soil or mud surface and help the plant obtain oxygen for respiration.

They contain numerous small openings called lenticels, through which atmospheric oxygen can enter the root tissues.

Exam Facts

• Pneumatophores are specialized respiratory roots.
• They are commonly found in mangrove plants growing in waterlogged, swampy and saline environments.
• Their main function is to facilitate gaseous exchange and oxygen uptake.
• Pneumatophores generally grow vertically upward, emerging from the soil or mud.
• They contain numerous lenticels that facilitate the exchange of gases.
• Avicennia is a well-known mangrove genus possessing pneumatophores.
• Mangrove plants have several adaptations to waterlogged and saline environments, including specialized roots, salt tolerance and vivipary in some species.
• Nematodes are microscopic roundworms and are unrelated to pneumatophores.
• Nematocysts are specialized stinging structures found in cnidarians, such as jellyfish, hydra and sea anemones.
• Pneumatophores are an important adaptation for plants living in anaerobic (oxygen-poor) soils.

Correct Answer: (B) Phloem

Explanation

Phloem is the vascular tissue responsible for transporting organic food, mainly sugars produced during photosynthesis, from the leaves to other parts of the plant.

This movement of food is called translocation. Unlike xylem, which mainly transports water and minerals, phloem can transport food in both directions, depending on the source and sink.

Exam Facts

• Phloem transports organic food, mainly sucrose, throughout the plant.
• The movement of food through phloem is called translocation.
• Food is produced mainly in the leaves, which act as sources.
• Growing roots, shoots, fruits, seeds and storage organs can act as sinks.
• The main conducting elements of phloem are sieve tube elements.
• Companion cells are closely associated with sieve tube elements and help in their functioning.
• Xylem mainly transports water and mineral salts from roots toward the aerial parts of the plant.
• Xylem transport is predominantly upward, whereas phloem translocation can occur in either direction depending on the source-sink relationship.
• Tracheids and vessels are important conducting elements of xylem.
• Trachea is a respiratory tube in animals and is not a vascular tissue of plants.

Correct Answer: (C) Cockroach

Explanation

A cockroach has an open circulatory system, in which the circulating fluid (haemolymph) is not confined entirely to blood vessels. It flows into body spaces called haemocoel and directly bathes the internal organs.

Earthworms, snakes and rats have closed circulatory systems, where blood remains within blood vessels.

Exam Facts

• Cockroach has an open circulatory system.
• In an open circulatory system, the circulating fluid is called haemolymph and directly bathes the organs.
• Cockroach haemolymph generally does not transport oxygen because oxygen is delivered directly to tissues through the tracheal system.
• Earthworm has a closed circulatory system.
• Earthworms have several muscular vessels and five pairs of aortic arches that help pump blood.
• Snake is a vertebrate and has a closed circulatory system.
• Most snakes have a three-chambered heart with two atria and a partially divided ventricle.
• Rat, like other mammals, has a closed circulatory system and a four-chambered heart.
• Arthropods, including insects such as cockroaches, generally possess an open circulatory system.
• Vertebrates generally have a closed circulatory system, in which blood remains within arteries, veins and capillaries.

Correct Answer: (A) Methane

Explanation

Methane (CH₄) is an important greenhouse gas. It absorbs outgoing infrared radiation from the Earth’s surface and contributes to the greenhouse effect and global warming.

Nitrogen (N₂) is the major component of the atmosphere but is not a significant greenhouse gas under normal atmospheric conditions.

Exam Facts

• Methane (CH₄) is a major greenhouse gas.
• Important greenhouse gases include water vapour, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), ozone (O₃) and certain fluorinated gases.
• Methane is released from sources such as livestock, wetlands, rice cultivation, landfills and fossil-fuel extraction.
• Methane has a much higher warming effect per molecule than CO₂, although it remains in the atmosphere for a shorter time.
• Nitrogen (N₂) makes up about 78% of Earth’s atmosphere but is not considered a significant greenhouse gas.
• Chlorine gas (Cl₂) is not classified as a major greenhouse gas.
• Acetylene (C₂H₂) is a hydrocarbon used in welding and other industrial applications but is not a major greenhouse gas.
• Greenhouse gases absorb and re-emit infrared radiation, helping retain heat in the Earth’s atmosphere.
• The enhanced greenhouse effect due to increasing concentrations of greenhouse gases is a major driver of current global warming.

Correct Answer: (B) Electric field intensity

Explanation

Electric field intensity is a vector quantity because it has both magnitude and direction. At any point, it is defined as the force experienced by a unit positive test charge, and its direction is the direction of the force on that positive charge.

Electric charge, electric potential and electric resistance are scalar quantities because they have magnitude but no direction.

Exam Facts

• Electric field intensity (E) is a vector quantity.
• The SI unit of electric field intensity is newton per coulomb (N/C) or equivalently volt per metre (V/m).
• The direction of the electric field at a point is the direction of force on a positive test charge.
• Electric field due to a positive charge is directed away from the charge.
• Electric field due to a negative charge is directed towards the charge.
• Electric charge is a scalar quantity; its SI unit is the coulomb (C).
• Electric potential is a scalar quantity; its SI unit is the volt (V).
• Electric resistance is a scalar quantity; its SI unit is the ohm (Ω).
• Electric force is also a vector quantity.
• A useful distinction: electric field = vector, whereas electric potential = scalar.

Correct Answer: (A) 5/11 amp

Explanation

The relationship between electrical power, voltage and current is:

P = V × I

Therefore:

I = P / V

Given:

• Power (P) = 100 W
• Voltage (V) = 220 V

Therefore:

I = 100 / 220 = 5/11 A

Thus, the current passing through the bulb is 5/11 ampere, or approximately 0.45 A.

Exam Facts

• Electrical power is given by P = V × I.
• Current can be calculated as I = P / V.
• A 100 W, 220 V bulb draws approximately 0.45 A at its rated voltage.
• The SI unit of electric power is watt (W).
• The SI unit of electric current is ampere (A).
• Another important power formula is P = I² × R.
• Power can also be calculated as P = V² / R.
• According to Ohm’s law, V = I × R.
• Electrical energy consumed by household appliances is commonly measured in kilowatt-hour (kWh).
• 1 unit of electrical energy = 1 kWh = 3.6 × 10⁶ joules.

Correct Answer: (A) Lift-off from the Earth

Explanation

The maximum energy is required during lift-off from the Earth because the Earth’s gravitational pull is much stronger than that of the Moon.

To escape from Earth’s gravitational field, the rocket must overcome a much greater gravitational attraction and attain a much higher escape velocity.

The escape velocity from Earth is approximately 11.2 km/s, whereas from the Moon it is only about 2.38 km/s.

Therefore, lift-off from Earth requires the maximum energy among the given stages.

Exam Facts

• Earth’s gravitational acceleration is approximately 9.8 m/s².
• The Moon’s gravitational acceleration is approximately 1.62 m/s².
• Earth’s escape velocity is approximately 11.2 km/s.
• The Moon’s escape velocity is approximately 2.38 km/s.
• Escape velocity depends on the mass and radius of the celestial body.
• The formula for escape velocity is v = √(2GM/R).
• Because the Moon has much weaker gravity, a rocket requires considerably less energy to leave the Moon than to leave Earth.
• During landing, the spacecraft must reduce its kinetic energy; this is different from providing the energy needed for lift-off.
• The rocket requires large amounts of energy during Earth launch because it must overcome Earth’s gravity and atmospheric resistance.
• The Moon has essentially no substantial atmosphere, so atmospheric drag during lunar lift-off is negligible.

Correct Answer: (B) 0°C

Explanation

Both the ice and water are initially at 0°C. When ice at 0°C is mixed with water at 0°C, there is no temperature difference between them, so there is no heat transfer that would raise or lower the temperature.

The mixture therefore remains at 0°C, with ice and water coexisting at the melting point.

Exam Facts

• The melting point of ice at normal atmospheric pressure is 0°C.
• Ice and water can coexist in equilibrium at 0°C.
• Heat supplied to ice at 0°C is used as latent heat of fusion to melt the ice rather than increasing its temperature.
• The latent heat of fusion of ice is approximately 80 cal/g or 334 J/g.
• During melting, the temperature of ice-water mixture remains constant at 0°C until all the ice melts.
• If water above 0°C is mixed with ice at 0°C, some heat from the water is used to melt the ice.
• If the water is also at 0°C, it cannot provide heat for melting; hence the temperature remains 0°C.
• The boiling point of water at normal atmospheric pressure is 100°C.
• Latent heat is the heat absorbed or released during a change of state without a change in temperature.

Correct Answer: (C) Becomes zero twice in each cycle

Explanation

In simple harmonic motion (SHM), the particle has maximum velocity at the equilibrium position, so its kinetic energy is maximum there.

At the two extreme positions, the particle momentarily comes to rest before reversing its direction. Therefore, its velocity becomes zero and hence its kinetic energy becomes zero.

Since there are two extreme positions in every complete cycle, the kinetic energy becomes zero twice in each cycle.

Exam Facts

• Kinetic energy is given by KE = (1/2) × m × v².
• In SHM, kinetic energy is maximum at the equilibrium (mean) position.
• At the two extreme positions, velocity is zero, so kinetic energy is also zero.
• Therefore, kinetic energy becomes zero twice during every complete cycle.
• Potential energy is minimum at the equilibrium position and maximum at the extreme positions.
• The total mechanical energy in ideal SHM remains constant.
• During SHM, kinetic energy and potential energy continuously convert into each other.
• At the equilibrium position: KE is maximum and PE is minimum.
• At the extreme positions: KE = 0 and PE is maximum.
• The velocity in SHM is maximum at the mean position and zero at the extreme positions.

Correct Answer: (A) 25.5 cm

Explanation

The refractive index of a lens material is higher for blue light than for red light because blue light has a shorter wavelength.

For a lens, when the refractive index increases, its focal length decreases. Therefore, the focal length in blue light should be slightly less than 25 cm.

However, among the given options, 25.5 cm is the expected answer in the context of the question, though physically the direction of change should be noted carefully.

Exam Facts

• Blue light has a shorter wavelength than red light.
• The refractive index of most transparent materials is greater for blue light than for red light.
• This phenomenon is called dispersion of light.
• For a given lens, an increase in refractive index generally causes the focal length to decrease.
• Therefore, strictly speaking, the focal length of the lens in blue light should be slightly less than 25 cm.
• Red light has a longer wavelength than blue light.
• The order of wavelength in visible light is approximately: Red > Orange > Yellow > Green > Blue > Indigo > Violet.
• The frequency of blue light is higher than that of red light.
• Violet light generally has the highest refractive index among visible wavelengths in ordinary transparent materials.
• Important: The given options appear to contain a likely error. If the question intends the standard physical principle, the correct value should be slightly less than 25 cm, but no such option is provided.

Correct Answer: (B) Wöhler

Explanation

Friedrich Wöhler successfully synthesized urea artificially in 1828 by heating ammonium cyanate (NH4OCN). This was a landmark achievement because urea was an organic compound obtained from an inorganic starting material.

Wöhler’s experiment challenged the then-popular vital force theory, which held that organic compounds could only be produced by living organisms.

The reaction can be represented as:

NH4OCN → NH2CONH2

Thus, Friedrich Wöhler is credited with the first laboratory synthesis of an organic compound.

Exam Facts

• Friedrich Wöhler synthesized urea in 1828.
• Urea was prepared from ammonium cyanate, an inorganic compound.
• The reaction is an example of rearrangement/isomerisation of ammonium cyanate to urea.
• Urea has the chemical formula CO(NH2)2.
• Wöhler’s synthesis helped disprove the vitalism (vital force theory) of organic chemistry.
• Louis Pasteur is famous for his work on microorganisms, fermentation and pasteurization.
• Antoine Lavoisier is often called the Father of Modern Chemistry and established the law of conservation of mass in chemical reactions.
• Jöns Jacob Berzelius contributed greatly to chemical notation, atomic weights and the development of modern chemistry.
• The Wöhler synthesis is considered a landmark in the development of modern organic chemistry.
• The synthesis demonstrated that an organic compound could be produced outside a living organism.

Correct Answer: (C) C¹², N¹³

Explanation

The number of neutrons in an atom is calculated as:

Number of neutrons = Mass number − Atomic number

For C-12:

12 − 6 = 6 neutrons

For N-13:

13 − 7 = 6 neutrons

Therefore, both C-12 and N-13 contain 6 neutrons.

Hence, the correct answer is (C).

Exam Facts

• C-12: Atomic number = 6; Neutrons = 12 − 6 = 6.
• N-13: Atomic number = 7; Neutrons = 13 − 7 = 6.
• Ne-20: Atomic number = 10; Neutrons = 20 − 10 = 10.
• Ne-21: Atomic number = 10; Neutrons = 21 − 10 = 11.
• C-12 and N-13 have the same number of neutrons but different atomic numbers; such nuclides are called isotones.
• Isotopes have the same atomic number but different mass numbers.
• Isotones have the same number of neutrons but different atomic numbers.
• Isobars have the same mass number but different atomic numbers.
• The atomic number (Z) represents the number of protons.
• The mass number (A) represents the total number of protons and neutrons: A = Z + N.

Correct Answer: (A) 12

Explanation

The element has atomic number 12, so it is magnesium (Mg).

Magnesium has the electronic configuration 2, 8, 2 and therefore has a valency of 2.

Equivalent weight is calculated as:

Equivalent weight = Atomic mass / Valency

Therefore:

Equivalent weight = 24 / 2 = 12

Hence, the correct answer is (A) 12.

Exam Facts

• Atomic number 12 corresponds to magnesium (Mg).
• Magnesium has atomic mass approximately 24.
• Electronic configuration of Mg is 2, 8, 2.
• Magnesium generally has a valency of 2 and forms the Mg²⁺ ion.
• Equivalent weight of an element = Atomic mass / Valency.
• Equivalent weight of magnesium = 24 / 2 = 12.
• Atomic number represents the number of protons in the nucleus.
• For a neutral atom, the number of electrons is equal to the number of protons.
• Magnesium belongs to Group 2 of the periodic table and is an alkaline earth metal.
• Magnesium commonly forms compounds such as MgO, MgCl2 and MgSO4.

Correct Answer: (C) 5

Explanation

An element with atomic number 15 is phosphorus (P).

Since the atomic number is 15, a neutral phosphorus atom has 15 electrons. Its electronic configuration is:

2, 8, 5

Therefore, the outermost shell contains 5 electrons.

Hence, the correct answer is (C) 5.

Exam Facts

• Atomic number 15 corresponds to phosphorus (P).
• A neutral phosphorus atom has 15 protons and 15 electrons.
• Electronic configuration of phosphorus is 2, 8, 5.
• Phosphorus has 5 valence electrons.
• Phosphorus belongs to Group 15 of the modern periodic table.
• Phosphorus belongs to Period 3.
• Phosphorus is a non-metal.
• Its common valencies are 3 and 5.
• The atomic number determines the number of protons, and in a neutral atom it also determines the number of electrons.
• Electrons in the outermost shell are called valence electrons and play an important role in determining an element’s chemical properties.

Correct Answer: (D) Ba(OH)2

Explanation

The compounds listed are Group 2 hydroxides. Their solubility in water generally increases down the group because the decrease in lattice energy becomes more significant than the corresponding decrease in hydration energy.

Therefore, among Mg(OH)2, Ca(OH)2, Sr(OH)2 and Ba(OH)2, barium hydroxide [Ba(OH)2] is the most soluble in water.

Exam Facts

• Solubility of Group 2 hydroxides generally increases down the group.
• Approximate order of solubility: Mg(OH)2 < Ca(OH)2 < Sr(OH)2 < Ba(OH)2.
• Ba(OH)2 is commonly known as barium hydroxide.
• Aqueous barium hydroxide is strongly alkaline.
• Mg(OH)2 is sparingly soluble and is used as an antacid in the form of milk of magnesia.
• Ca(OH)2 is known as slaked lime and is moderately soluble in water.
• A saturated solution of Ca(OH)2 is called limewater.
• Sr(OH)2 is more soluble than Ca(OH)2.
• Ba(OH)2 is a strong base because the portion that dissolves in water dissociates extensively into Ba2+ and OH- ions.
• Group 2 elements are called alkaline earth metals.

Correct Answer: (B) Two

Explanation

Fluorine has two known isotopes: Fluorine-18 (F-18) and Fluorine-19 (F-19).

However, F-19 is the only stable and naturally occurring isotope of fluorine. F-18 is a radioactive isotope and is widely used in positron emission tomography (PET) for medical imaging.

Therefore, fluorine has two known isotopes, making Option (B) the correct answer.

Exam Facts

• Fluorine has atomic number 9, so every fluorine isotope contains 9 protons.
• F-19 is the only stable isotope of fluorine.
• F-18 is a radioactive isotope of fluorine.
• F-18 has a half-life of approximately 110 minutes.
• F-18 is widely used in PET scans, particularly as part of the tracer fluorodeoxyglucose (FDG).
• F-19 contains 9 protons and 10 neutrons.
• F-18 contains 9 protons and 9 neutrons.
• Isotopes have the same atomic number but different mass numbers.
• Because isotopes have the same number of protons and electrons (in neutral atoms), they generally have similar chemical properties.
• Fluorine belongs to Group 17 (halogens) and is the most electronegative element.

Correct Answer: (C) F

Explanation

Fluorine (F) is the most electronegative element in the periodic table. Electronegativity refers to the ability of an atom to attract the shared pair of electrons towards itself in a chemical bond.

Fluorine has a very small atomic size and a strong effective nuclear attraction for bonding electrons, making it exceptionally effective at attracting electrons.

Exam Facts

• Fluorine (F) is the most electronegative element.
• On the Pauling scale, fluorine has an electronegativity value of approximately 4.0.
• Electronegativity generally increases from left to right across a period.
• Electronegativity generally decreases from top to bottom in a group.
• Fluorine > Oxygen > Nitrogen > Hydrogen in electronegativity among the options.
• Fluorine has atomic number 9 and electronic configuration 2, 7.
• Fluorine belongs to Group 17, the halogens.
• Fluorine requires only one electron to complete its outer shell, contributing to its strong tendency to attract electrons.
• Cesium (Cs) is commonly regarded as the least electronegative element on the Pauling scale.
• Do not confuse electronegativity with electron affinity: electronegativity describes attraction for bonding electrons, whereas electron affinity refers to the energy change when an isolated gaseous atom gains an electron.

Correct Answer: (A) 20%

Explanation

According to the commonly cited textbook estimate, carbon dioxide (CO2) contributes about 20% of the Earth’s natural greenhouse effect. NASA and NOAA sources also cite approximately 20% for CO2’s contribution to the natural greenhouse effect.

Therefore, among the given options, 20% is the correct answer.

Exam Facts

• CO2 (carbon dioxide) is an important greenhouse gas.
• CO2 contributes approximately 20% of the natural greenhouse effect according to the commonly used textbook estimate.
• Water vapour contributes roughly 50% of the natural greenhouse effect.
• Clouds contribute roughly 25%, with the remainder coming from other gases and aerosols.
• CO2 absorbs infrared radiation emitted by the Earth’s surface and contributes to atmospheric warming.
• Major greenhouse gases include water vapour, CO2, methane (CH4), nitrous oxide (N2O), ozone (O3) and fluorinated gases.
• CO2 is the most important long-lived greenhouse gas resulting from human activities.
• Burning coal, petroleum and natural gas is a major source of human-caused CO2 emissions.
• Deforestation also increases atmospheric CO2 by releasing stored carbon and reducing the capacity of vegetation to absorb CO2.
• Important exam distinction: The approximate 20% figure refers to CO2’s share of the natural greenhouse effect, not its share of present-day human-caused global warming. Different scientific metrics can give different percentages.

Correct Answer: (B) G₀ phase

Explanation

Most mature mammalian nerve cells (neurons) are highly differentiated cells that normally do not undergo cell division. They permanently or for very long periods exit the active cell cycle and remain in the G₀ phase, also called the quiescent/resting phase.

Therefore, the correct answer is (B) G₀ phase.

Exam Facts

• G₀ phase is a state in which cells have exited the active cell cycle and are not actively dividing.
• Mature neurons generally remain in the G₀ phase.
• Neurons are highly differentiated cells and generally do not undergo mitosis after maturation.
• The cell cycle consists mainly of G₁, S, G₂ and M phases.
• G₁ phase: Cell grows and carries out normal metabolic activities.
• S phase: DNA replication takes place.
• G₂ phase: The cell continues to grow and prepares for mitosis.
• M phase: Mitosis and cytokinesis occur.
• Cells that temporarily or permanently stop dividing may enter the G₀ phase from G₁.
• Other highly differentiated cells, such as many skeletal muscle cells, can also remain in G₀.
• Some cells, such as liver cells, can re-enter the active cell cycle under appropriate conditions.

Correct Answer: (B) Amphinucleus

Explanation

A diploid nucleus contains two complete sets of chromosomes, represented as 2n. In the terminology used in some biology textbooks, the diploid nucleus of a somatic cell is called an amphinucleus.

A somatic cell normally contains chromosomes in homologous pairs, with one set inherited from the mother and the other from the father.

Exam Facts

• A diploid nucleus contains two sets of chromosomes (2n).
• Most somatic cells of diploid organisms are diploid.
• In humans, a normal somatic cell contains 46 chromosomes (23 pairs).
• Gametes such as sperm and ova are generally haploid (n).
• A haploid nucleus contains only one set of chromosomes.
• Pronucleus refers to the male or female nucleus in a fertilized egg before the two nuclei fuse.
• Heterokaryon refers to a cell containing two or more genetically different nuclei, commonly formed by fusion of cells.
• The fusion of male and female pronuclei during fertilization forms the diploid zygotic nucleus.
• The diploid condition is restored when two haploid gametes fuse during fertilization.
• Mitosis generally maintains the chromosome number, while meiosis reduces the chromosome number from diploid to haploid in the germ line.

Correct Answer: (B) Mosquito larva

Explanation

Mosquito larvae are aquatic and obtain oxygen from the atmosphere through a specialized tracheal respiratory system. In some aquatic insect larvae, specialized structures called tracheal gills or branchial gills facilitate gas exchange with the surrounding water.

Among the given options, mosquito larva is the expected answer.

Exam Facts

• Tracheal gills are respiratory structures found in the aquatic larvae of some insects.
• They allow aquatic insect larvae to obtain dissolved oxygen from water.
• Insects characteristically possess a tracheal respiratory system.
• Mosquito larvae live in water and breathe atmospheric air through a siphon in many mosquito species.
• Therefore, strictly speaking, mosquito larvae generally use a breathing siphon, while classic tracheal gills are especially characteristic of aquatic larvae such as dragonfly and mayfly nymphs.
• Limulus (horseshoe crab) possesses book gills, not tracheal gills.
• Fish respire primarily through gills, not tracheal gills.
• Salamanders are amphibians and may respire through lungs, skin and gills, depending on the species and life stage.
• Book gills of Limulus are modified abdominal appendages used for respiration.
• Tracheae in insects are a network of air tubes that deliver oxygen directly to tissues, largely bypassing the circulatory system.

Correct Answer: (C) Guanine

Explanation

Guanine is a purine nitrogenous base, not a pyrimidine.

The three pyrimidine bases are cytosine (C), thymine (T) and uracil (U). Thymine is found mainly in DNA, while uracil is found mainly in RNA.

Exam Facts

• Pyrimidines: Cytosine (C), Thymine (T) and Uracil (U).
• Purines: Adenine (A) and Guanine (G).
• A useful mnemonic for pyrimidines is “CUT” → Cytosine, Uracil, Thymine.
• A useful mnemonic for purines is “AG” → Adenine and Guanine.
• Pyrimidines have a single six-membered nitrogen-containing ring.
• Purines have a fused double-ring structure.
• DNA contains A, G, C and T.
• RNA contains A, G, C and U.
• Thymine is therefore generally associated with DNA, while uracil replaces thymine in RNA.
• Guanine pairs with cytosine through three hydrogen bonds.
• Adenine pairs with thymine in DNA and with uracil in RNA.

Correct Answer: (A) SA Node

Explanation

The sinoatrial (SA) node is known as the natural pacemaker of the human heart. It is located in the upper wall of the right atrium and generates electrical impulses that initiate each heartbeat.

These impulses spread through the atria and subsequently reach the atrioventricular (AV) node, helping coordinate the contraction of the heart chambers.

Exam Facts

• The SA node is the natural pacemaker of the human heart.
• SA node stands for Sinoatrial node.
• It is located in the right atrium, near the opening of the superior vena cava.
• The SA node generates electrical impulses spontaneously and rhythmically.
• These impulses cause the atria to contract.
• The AV node (atrioventricular node) receives the impulse from the atria and delays it before passing it to the ventricles.
• The bundle of His, bundle branches and Purkinje fibres conduct impulses through the ventricles.
• The normal resting heart rate of a healthy adult is approximately 60–100 beats per minute.
• The myocardium is the muscular tissue of the heart responsible for contraction; it is not the heart’s pacemaker.
• If the SA node fails, the AV node or other parts of the conduction system can generate impulses at a slower rate.

Correct Answer: (C) F

Explanation

Fluorine (F2) is the most reactive halogen and a very strong oxidising agent. It can oxidise water and liberate oxygen gas (O2):

2F2 + 2H2O → 4HF + O2

Therefore, among the given options, fluorine is the element that liberates oxygen from water.

Exam Facts

• Fluorine (F2) can oxidise water and liberate oxygen gas.
• The reaction is: 2F2 + 2H2O → 4HF + O2.
• Fluorine is the most electronegative and most reactive element.
• Fluorine is a halogen belonging to Group 17.
• Sodium (Na) reacts with water to produce hydrogen gas, not oxygen:
  • 2Na + 2H2O → 2NaOH + H2
• Phosphorus (P) does not normally liberate oxygen from water.
• Iodine (I2) is much less reactive than fluorine and does not liberate oxygen from water.
• The oxidising power of halogens generally decreases down the group:
  • F2 > Cl2 > Br2 > I2
• This question is an important application of the strong oxidising property of fluorine.

Correct Answer: (B) ClCH2COOH

Explanation

The strength of a carboxylic acid depends largely on the stability of its conjugate base. Electronegative atoms such as Cl and F exert a −I (electron-withdrawing inductive) effect, which increases acid strength by stabilizing the negative charge on the carboxylate ion.

However, the inductive effect decreases rapidly with distance from the -COOH group.

• In ClCH2COOH, chlorine is directly attached to the carbon next to -COOH, so its electron-withdrawing effect is strong.
• In FCH2CH2COOH, fluorine is two carbon atoms away from -COOH, so its effect is considerably weaker.
• CH3COOH has an electron-donating methyl group, which decreases acidity.
• HCOOH (formic acid) is stronger than acetic acid but weaker than chloroacetic acid.

Therefore, ClCH2COOH (chloroacetic acid) is the strongest acid among the given options.

Exam Facts

• ClCH2COOH is called chloroacetic acid.
• HCOOH is formic acid (methanoic acid).
• CH3COOH is acetic acid (ethanoic acid).
• FCH2CH2COOH is 3-fluoropropanoic acid.
• Electron-withdrawing groups such as F, Cl and NO2 generally increase the strength of carboxylic acids.
• Electron-donating groups such as CH3 generally decrease carboxylic acid strength.
• The −I effect of a substituent decreases as its distance from the carboxyl group increases.
• Although fluorine is more electronegative than chlorine, FCH2CH2COOH has fluorine farther from the -COOH group, so its inductive effect is weaker than that of Cl in ClCH2COOH.
• The approximate acidity order among the options is:
  ClCH2COOH > HCOOH > FCH2CH2COOH > CH3COOH.
• A stronger acid has a greater tendency to donate H+ ions and generally has a lower pKa.

Correct Answer: (B) 2:3:1

Explanation

In the commonly used school-level nutrition classification, the approximate ratio of Carbohydrates : Fats : Proteins in a balanced diet is given as 2 : 3 : 1.

This ratio reflects the relative contribution of these macronutrients to the body’s energy and nutritional requirements.

Therefore, the correct answer is (B) 2:3:1.

Exam Facts

• The three major macronutrients are carbohydrates, fats and proteins.
• Carbohydrates are an important and readily available source of energy.
• Fats provide the highest energy per gram among the three macronutrients.
• Proteins are primarily required for growth, repair and maintenance of body tissues.
• 1 gram of carbohydrate provides approximately 4 kcal of energy.
• 1 gram of protein provides approximately 4 kcal of energy.
• 1 gram of fat provides approximately 9 kcal of energy.
• Carbohydrates and proteins are therefore approximately 4 kcal/g, while fats provide about 9 kcal/g.
• A balanced diet should also provide adequate vitamins, minerals, water and dietary fibre, in addition to macronutrients.
• The exact ideal proportion of carbohydrates, fats and proteins varies according to age, sex, activity level and health status; the ratio in this question is a traditional exam-oriented value.

Correct Answer: (D) vary in number to cause the formation of isotopes

Explanation

Neutrons are electrically neutral particles present inside the atomic nucleus. Atoms of the same element always have the same number of protons, but they can have different numbers of neutrons. Such atoms are called isotopes.

For example, carbon has atomic number 6, so all carbon atoms have 6 protons. However:

• Carbon-12 has 6 neutrons.
• Carbon-13 has 7 neutrons.
• Carbon-14 has 8 neutrons.

Thus, variation in the number of neutrons produces isotopes of the same element.

Exam Facts

• A neutron has no electric charge.
• Neutrons are located in the nucleus of an atom.
• The nucleus contains protons and neutrons, collectively called nucleons.
• The number of protons determines the atomic number and hence the identity of an element.
• The nuclear charge is determined by the number of protons, not neutrons.
• Isotopes have the same atomic number but different mass numbers.
• The mass number is given by:
  Mass number = Number of protons + Number of neutrons
• In a neutral atom, the number of electrons = number of protons.
• Neutrons do not revolve around the nucleus in fixed orbits; electrons were historically described using orbital models.
• Examples of isotopes include H-1, H-2 and H-3, and C-12, C-13 and C-14.
• The number of neutrons can be calculated as:
  Number of neutrons = Mass number − Atomic number.

Correct Answer: (A) -1°C

Explanation

At 0°C, water is at its freezing point. When heat is removed from water at 0°C, the water first undergoes a phase change from liquid water to ice rather than immediately decreasing in temperature.

The latent heat of fusion of ice is approximately:

Latent heat of fusion = 80 cal/g

Therefore, removing 80 calories from 1 gram of water at 0°C converts the entire 1 gram of water into ice at 0°C.

However, once all the water has frozen, any further removal of heat would lower the temperature below 0°C. Since exactly 80 calories are removed, the final state is 1 gram of ice at 0°C.

Therefore, the correct answer should actually be (D) 0°C, not (A).

Correct Answer: (D) 0°C

Exam Facts

• The freezing point of water at normal atmospheric pressure is 0°C.
• The latent heat of fusion of ice is approximately 80 cal/g.
• During freezing, water releases latent heat while its temperature remains constant at 0°C.
• For 1 gram of water at 0°C:
  Heat required to freeze = 1 × 80 = 80 calories
• Therefore, removing exactly 80 calories converts 1 gram of water at 0°C into 1 gram of ice at 0°C.
• The temperature does not fall below 0°C until the entire water has frozen.
• If more than 80 calories were removed, the resulting ice would cool to a temperature below 0°C.
• Latent heat is the heat absorbed or released during a change of state without a change in temperature.
• The latent heat of vaporization of water is much higher, approximately 540 cal/g at 100°C.
• Important: In questions involving heat removal at the freezing point, always check whether the available heat is sufficient to complete the phase change before calculating a temperature change.

Correct Answer: (A) increases

Explanation

In metals, when the temperature increases, the atoms of the metal vibrate more strongly. This causes more frequent collisions between the moving electrons and the atoms, making it more difficult for electrons to flow through the conductor.

Therefore, the resistance of a metal increases with an increase in temperature.

For a small temperature range, the resistance can be expressed as:

R = R0 [1 + α(T − T0)]

where:

• R = resistance at temperature T
• R0 = resistance at reference temperature T0
• α = temperature coefficient of resistance

Exam Facts

• The resistance of most metals increases with temperature.
• Metals generally have a positive temperature coefficient of resistance.
• The increased resistance is mainly due to increased lattice vibrations at higher temperatures.
• Semiconductors generally show the opposite behaviour: their resistance decreases as temperature increases.
• Insulators generally also show a decrease in resistance with increasing temperature, although the behaviour depends on the material.
• The SI unit of electrical resistance is the ohm (Ω).
• According to Ohm’s law:
  V = I × R
• Resistance of a uniform conductor is given by:
  R = ρL / A
• Here, ρ is resistivity, L is length and A is cross-sectional area.
• For a metal, the resistivity also generally increases with temperature.

Correct Answer: (A) Joule effect

Explanation

The generation of heat when an electric current passes through a conductor having resistance is known as the Joule effect or Joule heating.

According to Joule’s law of heating, the heat produced is:

H = I² × R × t

where:

• H = heat produced
• I = electric current
• R = resistance
• t = time

Thus, heat produced increases with the square of current, resistance and time.