WBPSC Clerkship Science Previous Year Questions with Answers

Correct Answer: (A) 8 minutes

Sunlight takes about 8 minutes 20 seconds (about 499 seconds) to reach the Earth. This is the time light takes to cover about 149.6 million km (1 astronomical unit) at about 3 × 10^8 m/s, so the nearest option is 8 minutes.

Exam Facts

• Speed of light in vacuum = 2,99,792 km/s (about 3 × 10^5 km/s).
• Time = distance/speed = 1.496 × 10^8 km ÷ 3 × 10^5 km/s ≈ 499 s.
• 1 AU is the mean Earth-Sun distance, about 149.6 million km.
• Light from the Moon reaches Earth in about 1.3 seconds.
• Light from Proxima Centauri, the nearest star after the Sun, takes about 4.24 years.
• 2 minutes (option B) and 4 minutes (option C) are too short. Light would only cover about 36 and 72 million km.
• 16 minutes (option D) would mean a distance of about 2 AU, roughly twice the actual distance.
• Light from the Sun takes about 5.5 hours to reach Pluto.
• The Earth is nearest the Sun at perihelion (about 3 January) and farthest at aphelion (about 4 July).
• So the travel time varies slightly, from about 8 min 10 s to 8 min 27 s.

Correct Answer: (A) Nitrogen

Nitrogen is a primary macronutrient that plants need in large amounts. It is a part of proteins, amino acids, nucleic acids and chlorophyll. Manganese, copper and chlorine are micronutrients.

Exam Facts

• Primary macronutrients: N, P, K (nitrogen, phosphorus, potassium).
• Secondary macronutrients: calcium, magnesium, sulphur; together with C, H, O there are 9 macronutrients.
• Micronutrients: Fe, Mn, Cu, Zn, B, Mo, Cl, Ni.
• Lack of nitrogen causes chlorosis, the yellowing of older leaves, and stunted growth.
• Manganese (option B) activates enzymes in photosynthesis (splitting of water).
• Copper (option C) helps in redox enzymes; lack of it causes dieback in citrus.
• Chlorine (option D) helps in the water-splitting step and in osmotic balance.
• Legumes fix nitrogen through Rhizobium bacteria in their root nodules.
• Urea (46% N) is the most used nitrogen fertiliser in India.
• Macronutrients are generally present at more than 10 mmol per kg of dry matter.

Correct Answer: (D) Pressure

The bar is a unit of pressure. 1 bar = 10^5 pascal (Pa) = 100 kPa, which is very close to normal atmospheric pressure at sea level. It is a metric unit accepted for use with SI, though the SI unit of pressure is the pascal.

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Correct Answer: (D) Gamma-rays

Gamma rays have the highest frequency and the shortest wavelength of all electromagnetic waves, so they carry the most energy per photon. They are given out by radioactive nuclei and by violent events in space. Their frequency is above about 10^19 Hz.

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Correct Answer: (B) 2nd Law of Motion

The unit of force is defined from Newton’s Second Law of Motion, F = ma. 1 newton (N) is the force that produces an acceleration of 1 m/s² in a mass of 1 kg. The First Law only gives a qualitative idea of force (and inertia); the Second Law gives the way to measure force, so the standard answer is the 2nd Law.

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Correct Answer: (B) Birds

Ornithology is the scientific study of birds (Greek ornis = bird, logos = study). India’s most famous ornithologist is Dr. Salim Ali, known as the Birdman of India.

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Correct Answer: (D) Radon

Radon (Rn) is a radioactive noble gas whose emissions were used in radiotherapy, for example in “radon seeds” implanted into tumours (brachytherapy). Hence radon is the noble gas used in the treatment of cancer.

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Correct Answer: (A) Vitamin A

Deficiency of Vitamin A (retinol) causes night blindness (nyctalopia), because vitamin A is needed to make rhodopsin (visual purple) in the rod cells of the retina, which let us see in dim light.

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Correct Answer: (C) Personal Area Network

Bluetooth connects devices within a few metres of one person (phone, earphones, smartwatch, keyboard), so it is a Personal Area Network (PAN), more exactly a Wireless PAN (WPAN).

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Correct Answer: (A) Nerve cell

The nerve cell (neuron) is the longest cell of the human body. Its axon can be about 1 metre long, for example the motor neurons running from the spinal cord to the toes.

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Correct Answer: (D) Becquerel

The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration (decay) per second. It is named after Henri Becquerel, who discovered radioactivity in 1896.

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Correct Answer: (B) Kelvin

Kelvin is the SI unit of thermodynamic temperature, not energy. Joule is the SI unit of energy, and the electron-volt (eV) is a small unit of energy used in atomic physics.

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Correct Answer: (D) SO2 and NO2

Acid rain is caused mainly by sulphur dioxide (SO2) and nitrogen oxides (NO2/NOx). In the air these gases form sulphuric acid (H2SO4) and nitric acid (HNO3), which make rain acidic with a pH below 5.6.

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Correct Answer: (A) Newton’s First Law

When a bus starts suddenly, the lower body of a passenger moves with the bus, but the upper body tends to stay at rest due to inertia. So the passenger is pushed back, an example of inertia of rest described by Newton’s First Law, option (A).

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Correct Answer: (D) Lead

Lead is not a natural or essential element of the human body. It is a toxic heavy metal with no biological role, while copper, zinc and iodine are essential trace elements. Traces of lead can enter the body from pollution, but it is not a normal body constituent, which is why it is the answer.

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Correct Answer: (C) Asteroids

NASA’s Lucy spacecraft was launched on 16 October 2021 to study asteroids, especially the Jupiter Trojan asteroids that share Jupiter’s orbit around the Sun. It is the first mission to the Trojan asteroids and will visit more asteroids than any earlier mission.

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Correct Answer: (C) Barometer

A barometer is the instrument used to measure atmospheric pressure. The mercury barometer was invented by the Italian scientist Evangelista Torricelli in 1643.

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Correct Answer: (A) 7·4

The pH of human blood is about 7.4 (normal range 7.35–7.45), so blood is slightly alkaline. This narrow range is kept steady mainly by the carbonic acid–bicarbonate buffer system, with help from the lungs and kidneys.

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Correct Answer: (B) Isaac Newton

The official key credits Sir Isaac Newton, whose three laws of motion (published in Principia, 1687) form the basis of the equations of motion. For uniform acceleration these are v = u + at, s = ut + ½at² and v² = u² + 2as; Galileo had earlier studied uniformly accelerated motion, but among the options Newton is the accepted answer.

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Correct Answer: (A) Joule (J)

The work function is the minimum energy needed to remove an electron from the surface of a metal. Since it is an energy, its SI unit is the joule (J), though it is usually quoted in electron volts (eV).

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Correct Answer: (C) Solar energy

Solar energy is a renewable, clean source that releases no greenhouse gases when it produces power, so it does not cause global warming. Burning fossil fuels, petrol cars and deforestation all add carbon dioxide (CO2) to the atmosphere.

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Correct Answer: (A) Cation

An atom that loses (gives up) an electron has more protons than electrons and becomes a positively charged ion, called a cation (e.g. Na → Na⁺ + e⁻). The printed key also gives (A) cation; note that the Bengali wording is garbled and literally reads “which becomes an atom after giving up an electron”, which would point to an anion, but the intended question is clearly what an atom forms on losing an electron.

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Correct Answer: (C) 10^-9 metre

The prefix nano means 10^-9, so 1 nanometre (nm) = 10^-9 metre, one billionth of a metre. The nanometre is used to measure wavelengths of light and the size of atoms and molecules.

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Correct Answer: (B) CaO, H2O

CaO (calcium oxide) is an electrovalent (ionic) compound formed by transfer of electrons from Ca to O, and H2O (water) is a covalent compound formed by sharing of electrons, so (B) is the required pair. The printed key shows (C), but O2 and CH4 are both covalent, so the correct answer is (B).

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Correct Answer: (D) They will be unable to hear

Sound is a mechanical wave and needs a material medium (solid, liquid or gas) to travel. The Moon has no atmosphere, so the space between two astronauts is practically a vacuum and they cannot hear each other speak in any voice; they talk by radio.

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Correct Answer: (A) Electrical energy

The kilowatt-hour (kWh) is the energy used when a device of power 1 kilowatt works for 1 hour, so it is a unit of electrical energy, not power. 1 kWh = 1000 W × 3600 s = 3.6 × 10^6 joule, and it is the commercial “unit” shown on electricity bills.

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Correct Answer: (B) Reflection

A stethoscope works on the principle of multiple reflection of sound: the faint sound of the heartbeat is reflected again and again along the narrow rubber tube, so it reaches the doctor’s ears without spreading out and losing loudness. The printed key shows (D) Wave nature, but the correct answer is (B) Reflection, as given in NCERT and all standard books.

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Correct Answer: (B) C-14

The age of fossils, wood, bones and other once-living remains is found by radiocarbon dating, which uses the radioactive isotope carbon-14 (C-14). A living organism keeps a constant ratio of C-14 to C-12, and after death the C-14 decays with a half-life of about 5,730 years, so the remaining amount tells the age.

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Correct Answer: (B) Blue vitriol

Blue vitriol (copper sulphate pentahydrate, CuSO4·5H2O) is the classic example of a crystal that holds water of crystallisation: its blue crystals contain 5 water molecules, and on heating they lose this water and turn into white anhydrous CuSO4. The printed key shows (A) Sodium chloride, which is wrong because NaCl crystals contain no water of crystallisation; the question is also flawed because washing soda (option D, Na2CO3·10H2O) contains water of crystallisation too, so (B), the standard textbook example, is taken as the best answer.

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Correct Answer: (C) Physical and chemical change

When a candle burns, both physical and chemical changes take place. The wax melts and later solidifies again, which is a physical change, while the wax vapour burns in air to form carbon dioxide and water vapour with heat and light, which is a chemical change.

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Correct Answer: (C) Vitamin ‘C’

Scurvy is a deficiency disease caused by lack of Vitamin C (ascorbic acid), so it is prevented by Vitamin C. Its symptoms are bleeding and spongy gums, loose teeth, slow wound healing and joint pain, because Vitamin C is needed to make collagen.

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Correct Answer: (B) Nephron

The nephron is the structural and functional unit of the kidney; each human kidney has about one million nephrons, which filter blood and form urine. A nephron has a glomerulus inside Bowman’s capsule, followed by the tubule and the loop of Henle.

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Correct Answer: (C) ‘S’-phase

DNA replication takes place in the S-phase (synthesis phase) of interphase, when the amount of DNA in the cell doubles while the chromosome number stays the same. The cell cycle runs G1 → S → G2 → M.

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Correct Answer: (A) H2, CO and CH4

Coal gas, made by the destructive distillation of coal, burns and gives heat because of its combustible gases: hydrogen (H2, about 45–50%), methane (CH4, about 30–35%) and carbon monoxide (CO, about 5–10%). Small amounts of non-combustible nitrogen and carbon dioxide are also present.

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Correct Answer: (A) 0.01 mg/litre

The WHO guideline value for arsenic in drinking water is 10 micrograms per litre, which equals 0.01 mg/litre (in force since 1993). The printed key shows (C) 0.001 mg/litre, but that is only 1 microgram per litre, so the correct answer is (A) 0.01 mg/litre.

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Correct Answer: (A) Sodium

Of the options, sodium is the element with only one stable (naturally occurring) isotope, sodium-23, so it is treated as having no isotope in standard keys. Uranium, carbon and chlorine all occur naturally as mixtures of two or more isotopes. Strictly, sodium does have short-lived radioactive isotopes (made artificially), but it is monoisotopic in nature, so (A) is the intended answer.

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Correct Answer: (C) Third class lever

In a third class lever, the effort lies between the fulcrum and the load, so the effort arm is always shorter than the load arm. Therefore its mechanical advantage (MA) is always less than 1. Such levers trade force for speed and range of movement, e.g. forceps, tongs and the human forearm.

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Correct Answer: (A) Nuclear fusion

The Sun’s enormous energy comes from nuclear fusion in its core, where hydrogen nuclei fuse to form helium. The small loss of mass in each reaction is converted into energy according to Einstein’s E = mc^2. The core temperature of about 15 million °C makes this fusion possible.

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Correct Answer: (B) Hydrogen

The ordinary hydrogen atom (protium, ¹H) has just one proton and one electron and no neutron in its nucleus. It is the only stable atom without a neutron.

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Correct Answer: (B) Four times

Kinetic energy KE = ½mv², so KE is proportional to the square of velocity. If v is doubled, KE becomes 2² = 4 times the original.

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Correct Answer: (B) 90°

When the angle of incidence equals the critical angle, the refracted ray grazes along the boundary, so the angle of refraction is 90°. If the angle of incidence exceeds the critical angle, total internal reflection occurs.

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Correct Answer: (D) Petro-chemical

Artificial (synthetic) fibres such as nylon, polyester, acrylic and rayon-based fibres are products of the petro-chemical industry, which uses chemicals derived from crude oil and natural gas. Polymerisation of these petrochemicals produces the fibres.

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Correct Answer: (A) Liver

Urea is synthesised in the liver through the ornithine (urea) cycle, which converts toxic ammonia from protein breakdown into less toxic urea. Urea is then carried by blood to the kidneys and excreted in urine.

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Correct Answer: (B) Nephron

The glomerulus is a tuft of blood capillaries inside Bowman’s capsule, and together they form the Malpighian body (renal corpuscle) of the nephron, the structural and functional unit of the kidney. Blood is filtered here under pressure, a process called ultrafiltration.

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Correct Answer: (C) Anaphase

In mitosis, the sister chromatids separate in anaphase, when the centromere of each chromosome splits and the spindle fibres pull the two chromatids to opposite poles. The printed key shows (B) Metaphase, but that is the stage when chromosomes line up at the equatorial (metaphase) plate; separation happens in anaphase.

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Correct Answer: (B) —C(=O)—NH—

A peptide bond is the amide linkage –CO–NH– that joins two amino acids. It forms when the carboxyl group (–COOH) of one amino acid reacts with the amino group (–NH2) of another, with loss of one molecule of water (a condensation or dehydration reaction).

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Correct Answer: (B) Electro-magnetic wave

Gamma (γ) rays are electromagnetic waves of the highest frequency and shortest wavelength. They carry no charge and no mass, travel at the speed of light, and are given out by radioactive nuclei.

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Correct Answer: (A) 125 Newton

By Newton’s second law of motion, Force = mass × acceleration (F = ma). Here F = 25 kg × 5 m/s² = 125 N, so the force is 125 newton.

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