General Science Previous Year Questions (PYQ) with Answers – Page 3

The correct answer is B, Aluminium. Aluminium naturally forms a thin layer of aluminium oxide when it is exposed to air, and this layer protects it from further corrosion. In anodising, the layer is made thicker on purpose. A clean aluminium article is made the anode, the positive electrode, in an electrolytic bath of dilute sulphuric acid, and the oxygen gas released at the anode reacts with the metal to build a thick oxide coat. This coat resists corrosion and scratches and can easily be dyed in attractive colours, which is why anodised aluminium is used for pressure cookers, window frames and many household articles. Option A is wrong because silver does not form a protective oxide coat; it turns black by forming silver sulphide. Option C is wrong because gold hardly reacts with air at all, so it needs no such coating. Option D is wrong because copper, in moist air, gets a green coat of basic copper carbonate, not an anodised oxide layer. Exam tip: anodising means a thick oxide layer on aluminium; galvanising means a coat of zinc on iron.

The correct answer is B, Dialysis. Haemodialysis uses a machine called an artificial kidney to clean the blood of a patient whose kidneys have failed. Blood is drawn from the patient, mixed with an anticoagulant such as heparin so that it does not clot, and passed through fine tubes with a semi-permeable lining that sit in a dialysing fluid. Waste products such as urea pass out through the lining into the fluid, and the cleaned blood is returned to the body through a vein. A person with complete kidney failure needs this treatment regularly, often two or three times a week, unless a kidney transplant is done. The Dutch doctor Willem Kolff built the first working artificial kidney in 1943. Option A is wrong because excretion is the body's own natural removal of wastes, which healthy kidneys perform. Option C is wrong because perspiration means sweating through the skin. Option D is wrong because expulsion only means pushing something out; it is not the name of this treatment. Exam tip: the working unit of the kidney is the nephron, and the artificial kidney process is haemodialysis, which mainly removes urea.

The correct answer is A, Tin and copper. Bronze is made by melting copper and tin together, with copper as the main metal. It is harder than pure copper and does not corrode easily, so it has been used for statues, bells, medals and utensils for thousands of years. The Harappans cast the famous bronze figure of the 'dancing girl', and the Chola rulers of south India are known for their bronze idols such as Nataraja. An alloy is a mixture of a metal with other metals or with a non-metal, made to improve qualities like hardness, strength and resistance to rust. B is wrong because copper and zinc make brass, not bronze. C is wrong because aluminium and zinc do not make bronze; alloys of aluminium such as duralumin are used in aircraft. D is wrong because zinc and tin without copper do not form bronze. Exam tip: bronze, copper plus tin; brass, copper plus zinc; steel, iron plus carbon; stainless steel adds chromium and nickel.

The correct answer is B, Thyroid, Adrenal glands, Pituitary. The pituitary gland sends out hormones that order the thyroid and the adrenal glands to release their own hormones. The pituitary is a pea-sized gland attached to the base of the brain, and it is called the master gland because it controls several other endocrine glands. For example, it releases a thyroid-stimulating hormone that makes the thyroid produce thyroxine, and another hormone that makes the adrenal glands release theirs. NCERT's Class 8 science book notes that glands such as the thyroid and the adrenals secrete hormones on receiving a message from the pituitary. A is wrong because the pancreas releases insulin in response to blood sugar, and the thyroid does not command the other two. C is wrong because the testes and ovaries take their orders from the pituitary, not from the thyroid. D is wrong because the pituitary gives orders; it does not wait for orders from the thyroid. Exam tip: pituitary, master gland; thyroid, thyroxine; adrenal, adrenaline; pancreas, insulin.

The correct answer is A, Glass powder and red phosphorus. The rough strip of a safety matchbox is coated with powdered glass and a little red phosphorus, while the head of the matchstick carries antimony trisulphide and potassium chlorate. When the match is struck, friction turns some red phosphorus into white phosphorus. This reacts at once with the potassium chlorate in the head and produces enough heat to set the antimony trisulphide burning. Keeping the phosphorus on the box and the other chemicals on the stick is what makes the match safe. NCERT's Class 8 science book adds that early matches used white phosphorus, which proved dangerous for the workers who made them and for users. B is wrong because white phosphorus is not used on the rubbing surface of a safety match. C is wrong because magnesium is not part of the striking strip. D is wrong because neither potassium nor white phosphorus is found on the strip. Exam tip: box strip, red phosphorus plus glass powder; match head, antimony trisulphide plus potassium chlorate.

The correct answer is C, Insulin. The pancreas is both an exocrine gland, pouring digestive enzymes into the intestine, and an endocrine gland. Its endocrine part is made of small clusters of cells called the islets of Langerhans. The beta cells in these islets release insulin, which lowers blood sugar by helping body cells take in glucose and by making the liver store extra glucose as glycogen. When the body makes too little insulin, or cannot use it properly, blood sugar stays high, which is diabetes mellitus. Insulin was discovered in 1921 by Frederick Banting and Charles Best. Option A is wrong because adrenaline, the ‘fight or flight’ hormone, comes from the medulla of the adrenal gland. Option B is wrong because glucagon is made by the alpha cells of the same islets, and it raises blood sugar, the opposite of insulin. Option D is wrong because aldosterone comes from the adrenal cortex and helps the kidneys keep back sodium and water. Exam tip: alpha cells make glucagon and raise sugar; beta cells make insulin and lower it.

The correct answer is C, amount of water in cells. Each stoma is surrounded by two guard cells, and the pore opens or closes as these cells gain or lose water. When water flows into the guard cells they swell and become turgid; because their inner walls are thicker than the outer walls, they curve outward and the pore between them opens. When they lose water they become flaccid, straighten and close the pore. The movement of potassium ions into and out of the guard cells drives this flow of water. Stomata are the tiny pores, mostly on the lower surface of leaves, through which plants take in carbon dioxide, give out oxygen and lose water vapour in transpiration. Option A is wrong because the position of the nucleus does not control the pore. Option B is wrong because the protein make-up of the cells does not change to open or shut the stomata. Option D is wrong because only one factor, the water content, is the cause here. Exam tip: turgid guard cells open the stoma, flaccid guard cells close it.

The correct answer is B, Al₂O₃ and ZnO. Aluminium oxide and zinc oxide behave like a base with acids and like an acid with bases, so both are amphoteric. With hydrochloric acid, aluminium oxide gives aluminium chloride and water. With sodium hydroxide, zinc oxide gives sodium zincate and water. The word amphoteric comes from the Greek for 'both', which is the easiest way to remember it. Most metal oxides are basic, while oxides of non-metals such as carbon dioxide and sulphur dioxide are acidic. Other common amphoteric oxides are those of lead and tin. Option A is wrong because copper(II) oxide is a basic oxide; it reacts with acids but not with bases. Option C is wrong for the same reason, as it also pairs aluminium oxide with basic copper oxide. Option D is wrong because only one pair, B, has both oxides amphoteric. Exam tip: remember the amphoteric four as Al, Zn, Pb and Sn, that is aluminium, zinc, lead and tin.

The correct answer is C, Vitamin B1. Thiamin (thiamine) is vitamin B1, a water-soluble vitamin that helps the body turn carbohydrates into energy and keeps the nerves and heart working well. Its deficiency causes beriberi, a disease that weakens the muscles and nerves. It was once common among people who ate mostly polished rice, because polishing removes the thiamin-rich outer layer of the grain. Good sources are whole grains, pulses, nuts and yeast. Being water-soluble, it is not stored in the body for long and must come from the daily diet. A is wrong because vitamin B2 is riboflavin, whose deficiency causes cracks at the corners of the mouth. B is wrong because vitamin B3 is niacin, whose deficiency causes pellagra. D is wrong because vitamin B12 is cobalamin, which contains cobalt, and its deficiency causes pernicious anaemia. Exam tip: B1 thiamin and beriberi; B2 riboflavin; B3 niacin and pellagra; B12 cobalamin and pernicious anaemia.

The correct answer is C, Newtonian telescope. Isaac Newton built the first practical reflecting telescope in 1668. In it, light from the star falls on a large concave mirror at the bottom of the tube, and a small flat mirror set at 45 degrees near the top turns the light sideways to the eyepiece. Because the objective is a mirror and not a lens, there is no chromatic aberration, the colour fringing that lenses produce, and a mirror can be made much larger and lighter than a lens. Most big observatory telescopes are therefore reflectors. A, the Galilean telescope, is a refractor using a convex objective lens and a concave eyepiece lens. B, the Keplerian telescope, is also a refractor, with two convex lenses, and gives an inverted image. D, the Schmidt telescope, is a catadioptric design that combines a spherical mirror with a glass corrector plate, so it is not mirrors only. Exam tip: refractor means lenses (Galileo, Kepler), reflector means mirrors (Newton), Schmidt means a mirror plus a corrector lens.

The correct answer is B, A bottle opener. Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort. In a bottle opener the rim of the cap is the fulcrum at the tip, the cap being lifted is the load in the middle, and your hand applies the effort at the far end. Such levers always multiply force because the effort arm is longer; a wheelbarrow and a nutcracker work the same way. A, A pair of scissors, is a first class lever, with the pivot between the effort and the load. C, A cricket bat, is a third class lever: the lower hand applies the effort between the top hand, which acts as the fulcrum, and the ball. D, A bow and arrow, works by storing energy in the bent bow like a spring, not by placing the load between the fulcrum and the effort. Exam tip: first class has the fulcrum in the middle, second class the load in the middle, third class the effort in the middle.

The correct answer is C, Zinc. Galvanisation is the coating of iron or steel with a thin layer of zinc so that the iron underneath does not rust. Zinc sits above iron in the reactivity series, so even when the coating is scratched, zinc corrodes first and keeps protecting the iron; this is called sacrificial protection. The zinc layer is usually put on by dipping the article in molten zinc (hot-dip galvanising) or by electroplating. Galvanised sheets are used for roofs, water pipes, buckets and electricity poles. A, Gallium, is a rare, low-melting metal and is never used for rust protection. B, Aluminum, forms its own protective oxide layer, but coating iron with aluminium is not called galvanisation. D, Silver, is too costly and is less reactive than iron, so it would not protect it sacrificially. Exam tip: galvanisation means a zinc coating on iron; a tin coating on iron is called tinning.

The correct answer is D, [M L T⁻²]. Newton's second law gives force = mass × acceleration. Mass has the dimension [M], and acceleration is velocity divided by time, that is [L T⁻¹] ÷ [T] = [L T⁻²]. Multiplying, force = [M L T⁻²]. Its SI unit is the newton, 1 N = 1 kg m s⁻², and its CGS unit is the dyne, with 1 N = 10⁵ dyne. Weight, tension, thrust and friction are all forces, so they share the same dimensional formula, which is a favourite exam trick. Option A is wrong because [M⁰ L³ T⁰] is simply [L³], the dimension of volume. Option B is wrong because [M L⁻³ T⁰] is mass per unit volume, that is density. Option C is wrong because [M⁰ L T⁻¹] is length per unit time, the dimension of speed or velocity. Exam tip: build from the definition: velocity [L T⁻¹], acceleration [L T⁻²], force [M L T⁻²], work and energy [M L² T⁻²], power [M L² T⁻³], pressure [M L⁻¹ T⁻²].

The correct answer is B, Pellagra. Pellagra is caused by a lack of vitamin B3, niacin, also called nicotinic acid, and is remembered by the three Ds: dermatitis, a rough dark rash on skin exposed to sunlight, diarrhoea from the gut, and dementia from the nervous system; untreated, a fourth D, death, follows. It was common where maize was the staple food, because the niacin in maize is bound and hard to absorb and maize is poor in tryptophan, the amino acid from which the body makes niacin. Niacin is found in meat, fish, groundnuts, whole grains and pulses. Option A is wrong because anaemia comes from a shortage of iron, vitamin B12 or folic acid, not B3. Option C is wrong because beriberi is the deficiency disease of vitamin B1, thiamine, affecting nerves and the heart. Option D is wrong because scurvy, with bleeding gums, is caused by a lack of vitamin C, ascorbic acid. Exam tip: B1 = beriberi, B2 = cheilosis, B3 = pellagra, B12 = pernicious anaemia, C = scurvy, D = rickets.

The correct answer is D, 9. Period 2 holds the eight elements from lithium (3) to neon (10), and group 17 is the halogen column, whose members have seven electrons in the outer shell. The element that is both in period 2 and in group 17 is fluorine, with electronic configuration 2, 7, and atomic number 9. You can work it out without memorising: period 2 means two shells, group 17 means seven valence electrons, so the electrons are 2 + 7 = 9, and in a neutral atom the number of electrons equals the atomic number. Fluorine is the most electronegative element and the most reactive non-metal. A, 8, is oxygen, which is in period 2 but in group 16 with six valence electrons. B, 7, is nitrogen, period 2, group 15. C, 10, is neon, period 2, group 18, a noble gas with a full shell. Exam tip: for periods 2 and 3, atomic number = electrons in the inner shells plus the group's last digit; 2 + 7 gives fluorine, 10 + 7 gives chlorine (17).

The correct answer is C, may attract or repel. A magnet cannot be cut into a single north pole and a single south pole. The moment a bar magnet breaks, each piece becomes a complete magnet with a north pole at one end and a south pole at the other, because magnetism comes from the tiny magnetic domains inside the material. So what happens when the pieces are brought close depends only on which ends face each other. If the north end of one faces the south end of the other they attract, and if two like poles face each other they repel. A is wrong because attraction is only one of the two possible results. B is wrong for the same reason, as repulsion happens only with like poles facing. D is wrong because both pieces are still magnets and a force must act between them. Exam tip: magnetic poles always exist in pairs, so every broken piece of a magnet is a smaller full magnet.

The correct answer is C, remains same. Loudness and frequency are two different properties of sound. Loudness depends on the amplitude of the vibration, that is how far the vibrating part moves from its rest position, while frequency is the number of vibrations made in one second and is measured in hertz. Turning the volume up makes the speaker push the air harder, so the amplitude and therefore the loudness rise, but the tune still plays the same notes, so the frequency does not change. This is why the ringtone sounds stronger and not higher in pitch. A and B are wrong because a change in frequency would change the pitch, and a louder ringtone would then sound shriller or deeper, which does not happen. D is wrong because the relation is definite and well known, so it can certainly be decided. Exam tip: amplitude decides loudness, frequency decides pitch, and the speed of sound in air depends only on the medium.

The correct answer is A, During respiration. Plants respire day and night, breaking glucose down to release energy, and carbon dioxide is the waste product of that process. Photosynthesis does the opposite: the plant takes in carbon dioxide and water and, using sunlight trapped by chlorophyll, makes glucose while releasing oxygen as its waste product. During the day photosynthesis runs faster than respiration, so a green plant gives out oxygen on balance; at night only respiration continues, so carbon dioxide is released. These gases move in and out through the stomata of leaves and the lenticels of woody stems. B is wrong because photosynthesis uses carbon dioxide up instead of producing it. C is wrong for the same reason, as oxygen and not carbon dioxide is the waste of photosynthesis. D is wrong because transpiration is the loss of water vapour from the plant and involves no carbon dioxide. Exam tip: respiration takes oxygen and gives carbon dioxide; photosynthesis takes carbon dioxide and gives oxygen.

The correct answer is B, the same, opposite. The same magnet moves at the same speed in both cases, so the rate of change of magnetic flux through the coil is equal and the induced potential difference has the same magnitude. But turning the other pole towards the coil reverses the direction of the field through it, so the induced voltage takes the opposite sign. This follows from Faraday's law of electromagnetic induction, which says the induced emf equals the rate of change of flux, and from Lenz's law, which fixes the direction so that the induced current opposes the change causing it. A is wrong because the sign must flip once the pole facing the coil is reversed. C is wrong because the speed, and therefore the rate of flux change, is unchanged, so the two magnitudes match. D is wrong on both counts. Exam tip: speed decides how big the induced emf is, the field direction decides its sign - Faraday for magnitude, Lenz for direction.

The correct answer is A, Peacock. The peacock is a bird, and all birds, like mammals, have a heart of four chambers: two atria and two ventricles. Four chambers keep oxygen-rich blood and oxygen-poor blood completely apart, so the body gets fully oxygenated blood. Birds and mammals need this because they are warm-blooded and burn a great deal of energy to hold a steady body temperature; flight makes the demand greater still. Crocodiles are the only reptiles with a four-chambered heart. B is wrong because a sea horse is a fish and has a two-chambered heart, one atrium and one ventricle. C is wrong because a frog, being an amphibian, has three chambers, two atria and a single ventricle in which the two kinds of blood mix. D is wrong for the same reason as the sea horse. Exam tip: fish 2 chambers, amphibians and most reptiles 3, birds and mammals 4; the peacock is India's national bird.