General Science Previous Year Questions (PYQ) with Answers

The correct answer is B, Iron rod. An iron rod is a solid, and the force of attraction between particles is strongest in the solid state.

In a solid the particles sit close together in fixed positions and can only vibrate, so a solid keeps its shape, has a definite volume and can hardly be compressed. In a liquid the attraction is weaker, so the particles slide over one another and the liquid takes the shape of its vessel while keeping its volume. In a gas the attraction is weakest and the particles move freely at high speed, so a gas fills any container and is easily compressed. The same order explains why solids have the highest density and gases the lowest.

Option A is wrong because water is a liquid with medium attraction. Option C is wrong because alcohol is also a liquid, and it evaporates faster than water. Option D is wrong because oxygen is a gas, where the attraction between particles is the weakest of all.

Exam tip: force of attraction is solid greater than liquid greater than gas, and the freedom of particles runs the other way.

The correct answer is C, Breaking a chalk stick. Force has to be applied to break the chalk because its particles hold one another together, and that pull is the force of attraction between particles.

Every substance is made of particles that attract one another, and the strength of that attraction decides how hard a thing is to break. The attraction is strongest in solids, less in liquids and least in gases, which is why an iron rod needs a hammer, water can be separated with a finger and air offers no resistance at all. The school activity of breaking chalk, then a pencil and then an iron nail shows the difference in this force from one solid to another.

Option A is wrong because compressing a sponge only squeezes out the air in its pores. Option B is wrong because dissolving sugar shows diffusion and the spaces between particles. Option D is wrong because heating ice shows a change of state, not the attraction itself.

Exam tip: attraction between particles is strongest in solids, weaker in liquids and weakest in gases.

The correct answer is A, Aedes - Chikungunya - Bacteria. This set is wrong because chikungunya is caused by a virus, the chikungunya virus, and not by bacteria. It is spread by Aedes mosquitoes, the same day-biting mosquitoes that carry dengue and Zika, and it causes high fever with severe joint pain. The name comes from a word in the Makonde language of East Africa meaning 'that which bends up', describing patients bent over with pain. Aedes breeds in clean water stored in coolers, tyres, pots and tanks, which is why dengue and chikungunya cases rise after the monsoon. Option B is a correct set because the Culex mosquito spreads lymphatic filariasis, or elephantiasis, caused by parasitic worms such as Wuchereria bancrofti. Option C is correct because the female Anopheles mosquito spreads malaria, caused by the Plasmodium parasite, a protozoan. Option D is correct because Aedes also spreads dengue, which is caused by the dengue virus. Exam tip: Aedes carries dengue, chikungunya and Zika, all viruses; Anopheles carries malaria; Culex carries filariasis and Japanese encephalitis.

The correct answer is A, Protein. The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina. With age, and faster with diabetes, ultraviolet light, smoking or an injury, these proteins break down and clump together. The clumps scatter light, so the lens turns cloudy and vision becomes blurred, dim and glary. This clouding is a cataract, and it is one of the leading causes of blindness in India. It is treated by a short operation in which the cloudy lens is removed and replaced by an artificial intraocular lens. Option B is wrong because carbohydrate changes are not what clouds the lens, although high blood sugar in diabetes speeds up the protein damage. Option C is wrong because fat does not form the clear structure of the lens. Option D is wrong because the tear glands keep the eye moist and have nothing to do with the lens. Exam tip: cataract = cloudy lens from clumped proteins; glaucoma = raised pressure inside the eye.

The correct answer is C, Stapedius. The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body. When a very loud sound reaches the ear, the stapedius contracts and damps the vibration of the stapes, protecting the delicate inner ear; this is called the acoustic reflex. It is supplied by the facial nerve, so damage to that nerve can make ordinary sounds seem painfully loud. Option A is wrong because the biceps is a large muscle at the front of the upper arm that bends the elbow. Option B is wrong because the sartorius, which runs across the thigh, is the longest muscle of the body, not the smallest. Option D is wrong because the triceps at the back of the upper arm straightens the elbow and is a large muscle. Exam tip: smallest muscle stapedius, smallest bone stapes, longest muscle sartorius, largest muscle gluteus maximus.

The correct answer is B, milk of magnesia. Milk of magnesia is a milky white suspension of magnesium hydroxide, Mg(OH)2, in water. It is a mild base, so it neutralises the extra hydrochloric acid in the stomach that causes acidity and heartburn; the reaction gives magnesium chloride and water. In larger doses it draws water into the intestine and works as a laxative. This antacid is a textbook example of neutralisation, where an acid and a base react to form a salt and water. A is wrong because fused magnesia is magnesium oxide melted in an electric arc furnace and used as a heat-resistant material in furnace linings. C is wrong because magnesia alba is a basic magnesium carbonate, a white powder. D is wrong because caustic-calcined magnesia is magnesium oxide made by heating at lower temperatures and used in industry and farming. Exam tip: milk of magnesia is Mg(OH)2, an antacid base that neutralises stomach HCl.

The correct answer is B, 1831. In 1831 the British scientist Michael Faraday showed that a changing magnetic field produces an electric current in a nearby coil. He moved a magnet in and out of a coil of wire and saw a galvanometer needle move, and he also found that switching a current on and off in one coil induced a current in a second coil wound on the same iron ring. This is electromagnetic induction, the working principle of the electric generator (dynamo) and the transformer. The SI unit of capacitance, the farad, is named after him. A is wrong because 1853 is more than twenty years after the discovery. C is wrong because 1820 is the year Hans Christian Oersted found that an electric current produces a magnetic field, the reverse effect. D is wrong because 1875 has no link with this discovery. Exam tip: Oersted 1820, current makes magnetism; Faraday 1831, changing magnetism makes current.

The correct answer is C, Calcium oxychloride. Calcium oxychloride (CaOCl2) is bleaching powder, and the chlorine it releases removes colour from cotton and linen in the textile industry. It is made by passing chlorine gas over dry slaked lime, Ca(OH)2. When it reacts with water or a dilute acid it gives out chlorine, and this chlorine oxidises the colouring matter into colourless substances. Bleaching powder is also used to bleach wood pulp in paper mills and to disinfect drinking water, which is why it smells of chlorine. A is wrong because sodium carbonate is washing soda, used to remove the permanent hardness of water and in making glass. B is wrong because sodium hydrogencarbonate is baking soda, used in cooking and as an antacid. D is wrong because calcium chloride is a drying agent that absorbs moisture, not a bleach. Exam tip: bleaching powder CaOCl2, washing soda Na2CO3·10H2O, baking soda NaHCO3.

The correct answer is D, Golgi apparatus. The Golgi apparatus is the main site where glycoproteins and glycolipids are formed. It is a stack of flat, disc-shaped sacs called cisternae, first described by Camillo Golgi in 1898. Proteins made on the endoplasmic reticulum reach the Golgi, where sugars are added to them, and they are then packed into vesicles and sent to places inside the cell or out of it. That is why the Golgi is called the packaging and dispatch centre of the cell, and it also helps to form lysosomes. Option A is wrong because plastids, such as chloroplasts, carry out photosynthesis or store food and pigments in plant cells. Option B is wrong because lysosomes are small sacs of digestive enzymes and are called the suicide bags of the cell. Option C is wrong because mitochondria make energy in the form of ATP and are called the powerhouse of the cell. Exam tip: Golgi means packaging and adding sugars; mitochondria mean ATP; a lysosome is the suicide bag.

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is A, one coulomb per second. Electric current is the rate of flow of electric charge, written as I = Q/t, so one ampere flows when one coulomb of charge passes through a cross-section of a conductor in one second. One coulomb is the charge carried by about 6.25 × 10^18 electrons, so even a small current means a huge number of moving electrons. The ampere is one of the seven SI base units, and it is named after the French scientist André-Marie Ampère. Current is measured with an ammeter, which is always connected in series in a circuit, and small currents are expressed in milliamperes or microamperes. Option B is wrong because volt per second is not a unit of current; the volt measures potential difference. Option C is wrong because one joule per coulomb is the definition of one volt, the unit of potential difference. Option D is wrong because second per coulomb is the reverse of current and is not used as a unit at all. Exam tip: ampere = coulomb per second, volt = joule per coulomb, ohm = volt per ampere.

The correct answer is D, Heating effect. An iron, toaster, oven, kettle and heater all turn electrical energy into heat when current flows through a coil of high resistance. This is explained by Joule's law of heating: heat produced H = I²Rt, so the heat grows with the square of the current, with the resistance and with the time. The heating coils are made of nichrome, an alloy of nickel and chromium, because it has high resistance and does not melt or oxidise easily when red hot. The electric fuse and the filament bulb also work on this effect. A is wrong because the chemical effect of current is used in electroplating and in charging batteries. B is wrong because the magnetic effect runs electric bells, fans, motors and electromagnets. C is wrong because the physiological effect is the shock or muscle twitch that current causes in a living body. Exam tip: H = I²Rt; heater coil = nichrome, bulb filament = tungsten, fuse wire = tin-lead alloy with a low melting point.

The correct answer is C, a concave lens of suitable power. A concave lens spreads the light rays slightly before they enter the eye, so the image moves back onto the retina. In myopia, or short-sightedness, a person sees nearby objects clearly but distant objects look blurred. It happens when the eyeball is too long or the eye lens is too curved, so light from far objects meets in front of the retina. Concave lenses have negative power, so spectacles for myopia carry a minus number such as -2.0 D (dioptre). A is wrong because a biconvex lens brings rays together and would make the blur worse. B is wrong because a plain glass plate has no power and does not change where the rays meet. D is wrong because a convex lens corrects hypermetropia, or long-sightedness, in which the image forms behind the retina. Exam tip: Myopia = concave (minus) lens; Hypermetropia = convex (plus) lens; Presbyopia in old age = bifocal lens; Astigmatism = cylindrical lens.

The correct answer is B, Adrenal gland. Adrenaline is made by the adrenal glands, which sit like caps on top of the two kidneys. It is released in fear, anger or sudden danger, so it is called the "fight or flight" hormone. It raises the heartbeat and breathing rate, increases blood sugar and sends more blood to the muscles so that the body can react fast. Adrenaline comes from the inner part of the gland, the adrenal medulla; the outer part, the cortex, makes cortisol and aldosterone. A is wrong because the thyroid gland in the neck makes thyroxine, which controls metabolism and needs iodine. C is wrong because the pineal gland in the brain makes melatonin, which controls the sleep-wake cycle. D is wrong because the pituitary gland makes growth hormone and controls several other glands, so it is called the master gland. Exam tip: Adrenal = adrenaline (emergency hormone), Thyroid = thyroxine (metabolism), Pancreas = insulin (blood sugar), Pituitary = master gland.

The correct answer is B, Na₂CO₃·10H₂O. Washing soda is sodium carbonate decahydrate: each unit of sodium carbonate holds ten molecules of water of crystallisation. It is made from common salt in steps: baking soda is heated to get anhydrous sodium carbonate, called soda ash, which is then recrystallised from water to give washing soda crystals. It is a basic salt used for cleaning, in the glass, soap and paper industries, and to remove the permanent hardness of water. Paper setters like to put these related compounds side by side as options, so learn them together. A is wrong because NaHCO₃ is baking soda (sodium hydrogencarbonate), used in cooking and in antacids. C is wrong because Na₂CO₃ without water is soda ash, not the crystals called washing soda. D is wrong because NaCl is common salt, the starting material for all of these. Exam tip: NaCl → NaHCO₃ (baking soda) → Na₂CO₃ (soda ash) → Na₂CO₃·10H₂O (washing soda).

The correct answer is A, Red light has a longer wavelength and is scattered the least, making it visible from a distance. Red has the longest wavelength in visible light, about 700 nm, so the tiny particles of air, fog, smoke and dust scatter it the least. The light therefore travels far without fading and can be seen from a distance, which is exactly what a danger signal needs. This follows Rayleigh scattering: the shorter the wavelength, the more the light is scattered. The same idea explains why the clear sky looks blue, since blue light is scattered the most, and why the sun looks red at sunrise and sunset. B is wrong because red light is not more reflective than other colours. C is wrong because how easily a colour is produced has nothing to do with its use in signals. D is wrong because looks are not the scientific reason. Exam tip: longest wavelength = least scattering = red for danger; shortest wavelength = most scattering = blue sky.

The correct answer is D, Potassium. The reactivity series lists metals from the most reactive to the least reactive, and potassium heads it because it loses its single outer electron most easily. It reacts so violently with cold water that the hydrogen released catches fire, so potassium is stored under kerosene. The common order is K, Na, Ca, Mg, Al, Zn, Fe, Pb, (H), Cu, Hg, Ag, Au. A metal higher in the list pushes a lower metal out of its salt solution, which is why an iron nail kept in blue copper sulphate solution gets a brown coat of copper. Metals above hydrogen give hydrogen gas with dilute acids; those below it do not. A is wrong because copper lies below hydrogen and does not react with dilute acids. B is wrong because iron sits in the middle of the series. C is wrong because silver is near the bottom, just above gold. Exam tip: top = potassium, bottom = gold; K and Na are kept under kerosene.

The correct answer is D, Fleming's Left-Hand Rule. It gives the direction of the force, and so of the motion, on a current-carrying conductor placed in a magnetic field, which is exactly what turns the coil of a motor. Stretch the thumb, forefinger and middle finger of the left hand so that they are at right angles to one another. If the forefinger points along the magnetic field and the middle finger along the current, the thumb points in the direction of the force. The force is greatest when the current is at right angles to the field. A is wrong because Ampere's law relates the magnetic field around a closed loop to the current passing through it. B is wrong because the right-hand thumb rule finds the direction of the magnetic field lines around a straight current-carrying wire. C is wrong because Fleming's right-hand rule gives the direction of the induced current in a generator. Exam tip: left hand for motor, right hand for generator; forefinger = field, middle finger = current, thumb = motion.

The correct answer is A, CH₄ + 2O₂ → CO₂ + 2H₂O. Combustion means burning in oxygen, and complete burning of methane gives carbon dioxide, water, heat and light. The equation is balanced: one carbon, four hydrogen and four oxygen atoms on each side. Methane is the simplest hydrocarbon and the main gas in natural gas, CNG and biogas, which is why it burns with a clean blue flame in stoves and vehicles. When oxygen is short, burning is incomplete and poisonous carbon monoxide forms instead of carbon dioxide. B is wrong because it is a substitution reaction: in sunlight chlorine replaces a hydrogen atom of methane, and nothing burns. C is wrong because it is not balanced and shows carbon monoxide, the product of incomplete burning. D is wrong because methane reacting with steam, not oxygen, to give carbon monoxide and hydrogen is steam reforming, an industrial way to make hydrogen. Exam tip: complete combustion of any hydrocarbon gives CO₂ + H₂O + energy.

The correct answer is A, The pressure in blood vessels exceeds outside pressure. At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level. The blood inside our vessels keeps pushing outwards at nearly its usual pressure. In the nose the blood vessels are very fine and lie close to the surface, so when the pressure inside them becomes greater than the pressure outside, some of them burst and the nose bleeds. The cold, dry mountain air also makes the lining of the nose crack more easily. The same fall in air pressure is why water boils below 100 °C on mountains and food takes longer to cook. B is wrong because the pressure inside the vessels becomes more than, not less than, the outside pressure. C is wrong because equal pressures would give no push to burst the vessels. D is wrong because blood does not become thick enough at a height to cause nose bleeding. Exam tip: higher altitude, lower air pressure, so the pressure in blood vessels is relatively higher and the nose can bleed.