General Science Previous Year Questions (PYQ) with Answers – Page 5

The correct answer is C, erect, virtual and larger than the object. For a lens, magnification m is the image height divided by the object height, which also equals v divided by u. A plus sign means the image is erect and virtual, and a value of 2 means it is twice as tall as the object. Only a convex lens can form such an image, when the object is placed between the optical centre and the principal focus; this is exactly how a magnifying glass or a simple microscope works. A concave lens also forms erect, virtual images, but they are always smaller, so its magnification stays between 0 and plus 1. A is wrong, because an erect, virtual, smaller image needs m between 0 and 1, as with a concave lens. B is wrong, because a real, inverted image always has a negative magnification. D is wrong, because a real, inverted, enlarged image would have m below minus 1, such as minus 2. Exam tip: the sign tells the type, plus for virtual and erect, minus for real and inverted; a value above 1 means enlarged.

The correct answer is C, refraction of starlight. Starlight has to cross many layers of air before it reaches the eye, and these layers keep changing in temperature and density, so their refractive index keeps changing too. The light is bent a little differently every moment, the apparent position of the star shifts slightly and the amount of light entering the eye rises and falls. This flickering is what we call twinkling. A star is so far away that it acts as a point source, so the small shifts are easily seen. Planets are nearer and appear as tiny discs; light from the many points of the disc averages out, so planets do not twinkle. A, Diffraction, is the bending of light around edges and is not the cause. B, Reflection, sends light back from a surface and cannot make a star flicker. D, Scattering, of sunlight by air makes the sky blue but does not cause twinkling. Exam tip: twinkling and the early sunrise both come from atmospheric refraction; the blue sky and the red sunset come from scattering.

The correct answer is A, Night blindness. Vitamin A, chemically retinol, is needed to make rhodopsin, the light-sensitive pigment in the rod cells of the retina that lets us see in dim light. When the vitamin is short, the eye cannot adjust to darkness, and the person cannot see properly at night or in poor light; this is night blindness (nyctalopia). If the deficiency continues, the eye becomes dry and the cornea is damaged, a condition called xerophthalmia, which can end in total blindness. Vitamin A is fat-soluble and comes from carrots, papaya, mango, green leafy vegetables, milk, eggs and fish liver oil. B is wrong because scurvy, with bleeding gums, is caused by lack of vitamin C. C is wrong because marasmus is caused by a severe shortage of both calories and protein in young children. D is wrong because kwashiorkor is a protein deficiency disease marked by a swollen belly. Exam tip: vitamin A night blindness, C scurvy, D rickets, K bleeding; marasmus and kwashiorkor are protein-energy problems, not vitamin diseases.

The correct answer is C, 82. Lead has 82 protons in its nucleus, so its atomic number is 82. Its symbol is Pb, from the Latin plumbum, the root of the word "plumber", because Roman water pipes were made of lead. It sits in group 14 and period 6 of the periodic table, below carbon, silicon, germanium and tin, and it is the heaviest element that has stable isotopes; the decay chains of uranium and thorium end at lead. Lead is soft, dense and poisonous, which is why it has been removed from petrol and paint, and it is used in car batteries and radiation shields. The four options are neighbours in the table, so the exam is testing the exact number. A, 81, is thallium (Tl). B, 78, is platinum (Pt). D, 79, is gold (Au). Exam tip: the run of heavy metals goes 78 platinum, 79 gold, 80 mercury, 81 thallium, 82 lead.

The correct answer is C, 277. Water is densest at about 4 degrees Celsius, and 4 plus 273 gives roughly 277 kelvin. Most liquids keep shrinking as they cool, but water behaves oddly: below 4 degrees Celsius it starts to expand again because its molecules begin forming the open, hexagonal pattern of ice. This anomalous expansion is why ice is lighter than water and floats, and why a lake freezes from the top while the 4-degree water sinks to the bottom, letting fish survive the winter. Its density at that point is very close to 1 gram per cubic centimetre. D is wrong because 273 kelvin is 0 degrees Celsius, the freezing point, where water is already less dense than at 4 degrees. A is wrong because 0 kelvin is absolute zero, where no liquid water can exist. B is wrong because 227 kelvin is about minus 46 degrees Celsius, far below freezing. Exam tip: maximum density of water at 4 degrees Celsius equals 277 K; freezing at 273 K, boiling at 373 K.

The correct answer is C, Zn. Zinc has atomic number 30, meaning every zinc atom has 30 protons in its nucleus. It is the last element of the first transition series in period 4 of the modern periodic table, with the electronic configuration [Ar] 3d10 4s2, and it is placed in group 12. Zinc is a bluish-white metal used to galvanise iron against rust, to make brass with copper, and in dry cells. All four options are neighbours in the same period, which is why paper setters like this question: iron is 26, cobalt 27, nickel 28, copper 29 and zinc 30. A is wrong because Ni, nickel, has atomic number 28. B is wrong because Fe, iron, has atomic number 26. D is wrong because Co, cobalt, has atomic number 27. Exam tip: remember the run Fe 26, Co 27, Ni 28, Cu 29, Zn 30.

The correct answer is B, sulphurous acid. Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3. Sulphur dioxide is an oxide of a non-metal, and such oxides are acidic in nature, which is why the solution turns blue litmus red. The same gas, released when coal and diesel burn, dissolves in rain water in the air and is then slowly oxidised further, so sulphur dioxide is one of the main causes of acid rain. A is wrong because sulphur trioxide is made by oxidising sulphur dioxide with more oxygen over a catalyst, not by dissolving it in water. C is wrong because sulphuric acid is formed when sulphur trioxide, and not sulphur dioxide, meets water. D is wrong because sulphur is the element itself and cannot be got back simply by dissolving its oxide. Exam tip: SO2 with water gives H2SO3; SO3 with water gives H2SO4.

The correct answer is D, A and D. Vitamins A, D, E and K dissolve in fat, while the B group and vitamin C dissolve in water. Fat-soluble vitamins are absorbed along with the fat in our food and are stored in the liver and fatty tissue, so the body can build up a reserve; for the same reason, too much of them, especially A and D taken as supplements, can be harmful. Most water-soluble vitamins are not stored in large amounts, the extra is passed out in urine, and so they must be eaten regularly. Vitamin A keeps the eyes healthy and its lack causes night blindness, while vitamin D is made in the skin in sunlight and its lack causes rickets in children. Option A is wrong because vitamin B12 is water-soluble, even though D is fat-soluble. Option B is wrong because vitamin C is water-soluble. Option C is wrong because it pairs fat-soluble A with water-soluble C. Exam tip: remember the fat-soluble group as 'ADEK'; the B group and C are water-soluble.

The correct answer is B, Flavour enhancer. Monosodium glutamate is the sodium salt of glutamic acid, an amino acid, and it is added to soups, sauces, noodles and snacks to strengthen their savoury taste. This taste, called umami, is the fifth basic taste after sweet, sour, salty and bitter; it was identified in 1908 by the Japanese chemist Kikunae Ikeda, who first made MSG from a seaweed broth. In India MSG is widely sold as Ajinomoto, the name of the Japanese company that makes it. Option A is wrong because colour enhancers are food colours such as caramel or permitted dyes, which change how food looks, not how it tastes. Option C is wrong because preservatives such as sodium benzoate, or salt and vinegar, stop food from spoiling. Option D is wrong because emulsifiers such as lecithin help oil and water stay mixed in foods like mayonnaise and ice cream. Exam tip: MSG gives the umami flavour, sodium benzoate preserves, lecithin emulsifies.

The correct answer is C, Anabaena. Anabaena is a cyanobacterium, a prokaryote with no true nucleus, and all prokaryotes are placed in Monera. In R.H. Whittaker's five-kingdom classification (1969), Monera holds the bacteria and the cyanobacteria, or blue-green algae, whose cells have no nuclear membrane and no membrane-bound organelles. Anabaena grows as chains of cells and has special thick-walled cells called heterocysts that fix nitrogen from the air. It lives inside the small water fern Azolla, which is why Azolla is used as a biofertiliser in paddy fields. Option A is wrong because diatoms are single-celled eukaryotes with glass-like silica walls, placed in Protista; their deposits form diatomaceous earth. Option B is wrong because Euglena is a protist that makes its own food in light but feeds like an animal in the dark. Option D is wrong because Ulothrix is a filamentous green alga with a true nucleus, grouped with plants. Exam tip: no true nucleus means Monera; Anabaena and Nostoc are the nitrogen-fixing cyanobacteria to remember.

The correct answer is C, Nitrogen. Nitrogen is an unreactive gas, so it drives the oxygen out of the packet and stops the oil in the chips from getting oxidised. Rancidity is the oxidation of fats and oils in food, which spoils their smell and taste. Chips are fried in oil, so they turn rancid quickly once they meet air. Filling the pack with nitrogen keeps oxygen out and also acts as a cushion that stops the chips from breaking in transport. Other ways to slow rancidity are adding antioxidants, storing food in airtight containers and keeping it in a refrigerator. Option A is wrong because carbon dioxide is used for fizzy drinks and some other foods, but the standard gas for chips is nitrogen, which is cheap and very unreactive. Option B is wrong because hydrogen is highly inflammable and unsafe inside food packs. Option D is wrong because oxygen is the very gas that causes rancidity in the first place. Exam tip: rancidity is oxidation of fats; nitrogen flushing and antioxidants prevent it.

The correct answer is C, 1 and 3 only. The cooking temperature is set by the pressure inside the cooker, and that pressure is fixed by the weight sitting on the vent and the area of the hole under it. The boiling point of water rises with pressure. In an open pan water boils at 100°C, but when steam is trapped, pressure builds up until it can lift the weight, the whistle, off the vent. Pressure is force divided by area, so a heavier weight or a smaller hole means a higher pressure before steam escapes, and water then boils at about 120°C, which is why food cooks faster. Statement 2 is wrong because a bigger flame only makes the water boil and the whistle blow sooner; once steam escapes, the temperature stays at the boiling point for that pressure, and extra heat just makes more steam. Statements 1 and 3 are right for the reason above. So options A, B and D, which include statement 2, are wrong. Exam tip: higher pressure means a higher boiling point; the flame changes the speed, not the temperature.

The correct answer is A, it is dipolar in nature. Water is called the universal solvent because its molecule is polar: the oxygen end carries a partial negative charge and the two hydrogen ends carry partial positive charges. The molecule is bent at an angle of about 104.5°, so these charges do not cancel out. When a salt such as sodium chloride is put in water, the negative oxygen ends surround the sodium ions and the positive hydrogen ends surround the chloride ions, pulling the crystal apart; this is called hydration. Water also forms hydrogen bonds with polar substances such as sugar and alcohol, which is why they dissolve easily, while non-polar oil does not. Option B is wrong because water is in fact a poor conductor of heat, and heat conduction has nothing to do with dissolving. Option C is wrong because high specific heat explains why water warms up slowly, not why it dissolves things. Option D is wrong because being an oxide of hydrogen does not by itself make a liquid a good solvent. Exam tip: polar water dissolves polar and ionic substances, because like dissolves like.

The correct answer is A, Melatonin. The pineal gland, a small pine-cone-shaped gland deep in the brain, secretes melatonin. Melatonin controls the body's day-night rhythm, called the circadian rhythm, and helps regulate sleep. The gland releases more melatonin in darkness and less in bright light, which is why bright screens late at night can disturb sleep. Melatonin also plays a part in the timing of puberty and in seasonal changes in some animals. The French philosopher Descartes once called the pineal gland 'the seat of the soul'. B is wrong because progesterone is made mainly by the ovaries (the corpus luteum) and helps prepare for and maintain pregnancy. C is wrong because epinephrine, or adrenaline, is released by the adrenal medulla and prepares the body for 'fight or flight'. D is wrong because insulin is made by the beta cells of the islets of Langerhans in the pancreas and lowers blood sugar. Exam tip: pineal gland, melatonin, sleep; pancreas, insulin; adrenal medulla, adrenaline.

The correct answer is B, Roasting. Roasting means heating a sulphide ore strongly in plenty of air, so that the sulphide turns into an oxide and the sulphur escapes as sulphur dioxide gas. The standard example is zinc blende: 2ZnS + 3O2 gives 2ZnO + 2SO2. An oxide is easier to reduce to the metal with carbon, which is why ores of zinc, lead and copper first pass through this step. Remember the key contrast: roasting uses excess air and suits sulphide ores, while calcination uses limited or no air and suits carbonate ores. A is wrong, because calcination heats carbonate ores such as calamine in limited air, as when ZnCO3 gives ZnO and CO2. C is wrong, because smelting is the later step in which the oxide is reduced to metal in a furnace with a reducing agent and a flux. D is wrong, because incineration is burning waste at a high temperature, not a step in extracting metals. Exam tip: sulphide ore, roasting, excess air; carbonate ore, calcination, little or no air.

The correct answer is A, B3. Pellagra is caused by a lack of vitamin B3, also called niacin or nicotinic acid. The body can also make niacin from the amino acid tryptophan, so the disease is common where people live mainly on maize, which is poor in both. Pellagra is remembered by the 'four Ds': dermatitis (rough, dark skin on parts exposed to the sun), diarrhoea, dementia and, if untreated, death. Niacin is found in meat, fish, groundnuts, whole grains and milk. B is wrong because vitamin B6 (pyridoxine) deficiency causes anaemia, skin problems and convulsions in infants. C is wrong because vitamin B2 (riboflavin) deficiency causes cracked lips and sores at the corners of the mouth, called ariboflavinosis. D is wrong because vitamin B12 (cobalamin) deficiency causes pernicious anaemia and nerve damage. Exam tip: B1 beriberi, B2 ariboflavinosis, B3 pellagra, B12 pernicious anaemia; pellagra = the four Ds.

The correct answer is B, Vitamin C. Vitamins fall into two groups: the water-soluble ones, which are vitamin C and the whole B-complex, and the fat-soluble ones, A, D, E and K. Vitamin C is ascorbic acid, found in citrus fruits, amla, guava and tomatoes; its deficiency causes scurvy, with bleeding gums and slow healing of wounds. Because water-soluble vitamins are not stored in the body and the extra is passed out in urine, they must be taken daily, while fat-soluble vitamins are stored in the liver and fatty tissue. A, Vitamin K, is fat-soluble and needed for blood clotting. C, Vitamin A, retinol, is fat-soluble and its deficiency causes night blindness. D, Vitamin D, calciferol, is fat-soluble, made in the skin in sunlight, and its lack causes rickets. Exam tip: remember "ADEK are fat-soluble"; everything else, B-complex and C, dissolves in water.

The correct answer is B, Pyrometer. A pyrometer measures very high temperatures, such as those of furnaces, kilns and molten metal, without touching the hot object. It works on the principle that every hot body gives off thermal radiation whose intensity and colour depend on its temperature; the instrument reads this radiation and converts it into a temperature value. Ordinary mercury thermometers stop at about 350 degrees Celsius, so steel plants, glass works and cement kilns rely on pyrometers, which can read well above 1,000 degrees Celsius. The word comes from the Greek pyro, meaning fire. A is wrong because a bolometer measures the power of incident electromagnetic radiation, such as infrared or microwaves, not furnace temperature. C is wrong because an ammeter measures electric current in amperes. D is wrong because a fluxmeter measures magnetic flux. Exam tip: pyrometer for furnace heat, thermometer for body heat, ammeter for current, fluxmeter for magnetism.

The correct answer is B, Absolute pressure. Absolute pressure is counted from the absolute zero of pressure, which is a perfect vacuum, so it can never be negative. The working relation is simple: absolute pressure equals gauge pressure plus atmospheric pressure. A tyre showing 30 units on a gauge is really at 30 plus the local atmospheric pressure. Option A is wrong because gauge pressure is measured above the atmospheric pressure of the place, which is why an ordinary pressure gauge reads zero when it is open to the air even though air is pressing on it. Option C is wrong because vacuum pressure, also called negative gauge pressure, is the amount by which a pressure falls below atmospheric. Option D is wrong because atmospheric pressure is the weight of the air column above a place and is about 101.325 kilopascal, equal to 760 millimetres of mercury or 1.01325 bar at sea level. Exam tip: absolute equals gauge plus atmospheric, and only absolute pressure starts from a perfect vacuum.

The correct answer is B. Potential difference between two points of a circuit is the difference in electric potential between them, and it equals the work done in moving a unit positive charge from one point to the other. In symbols V = W/Q, so the unit is the volt, and one volt means one joule of work for each coulomb of charge. Potential difference is the push that drives a current, it is measured with a voltmeter joined in parallel across the two points, and Ohm's law links it to current as V = IR. Option A is wrong because capacitance is the charge a capacitor stores for each volt applied, measured in farad; it is a property of the device, not a difference between points. Option C is wrong because current is the rate of flow of charge, measured in ampere by an ammeter placed in series, and in a series circuit it is the same everywhere. Option D is wrong because resistance opposes current and is measured in ohm. Exam tip: V = W/Q, voltmeter in parallel, ammeter in series.