General Science Mixed Quiz: Set 38

The correct answer is D, -40°. Only at -40 do the two scales read alike, so -40 °C and -40 °F are the very same temperature. The scales are linked by F = (9/5)C + 32. Writing C in place of F gives C = (9/5)C + 32, so -(4/5)C = 32 and C = -40. On the Celsius scale water freezes at 0° and boils at 100°, while on the Fahrenheit scale the same two points are 32° and 212°, so 100 Celsius divisions cover 180 Fahrenheit divisions. Because the two scales climb at different rates, they can agree at exactly one point, and that point lies well below both freezing marks. A is wrong because 0 °C equals 32 °F. B is wrong because -25 °C equals -13 °F. C is wrong because -37 °C comes to about -34.6 °F. Exam tip: remember the single crossing point -40 °C = -40 °F, and the freezing pair 0 °C = 32 °F.

The correct answer is A, hammer, anvil and stirrup. The middle ear holds three tiny bones, the smallest in the human body, called the malleus, the incus and the stapes, which in everyday English are the hammer, the anvil and the stirrup. Sound waves collected by the pinna travel down the ear canal and set the eardrum vibrating. The three ossicles pass that vibration along in a chain and amplify it about twenty times before handing it to the oval window of the cochlea, where the fluid inside converts it into nerve signals for the auditory nerve. The stapes is the smallest bone in the body, roughly 3 mm long. Option B is wrong because the cochlea is the spiral fluid-filled part of the inner ear, not a middle-ear bone. Option C is wrong because the pinna is the outer flap of the ear. Option D is wrong because there is no bone called the auditory bone. Exam tip: malleus, incus and stapes are the hammer, anvil and stirrup, and the stapes is the smallest bone in the human body.

The correct answer is D, between the 2nd and the 13th group, that is groups 3 to 12. The d-block sits in the middle of the periodic table, bridging the s-block on the left and the p-block on the right. Its members are called transition elements because the last electron entering the atom goes into a d-orbital of the penultimate shell. Ten vertical columns make up the block, so every long period from the fourth onwards carries ten such elements, beginning with scandium. Variable valency, coloured compounds, the forming of complexes and strong catalytic behaviour are the properties a paper setter tests here. A is wrong because group 18 is the noble gases, which belong to the p-block. B is wrong because group 8 is only one column of the block, holding iron, ruthenium and osmium. C is wrong for the same reason, since group 9 of cobalt, rhodium and iridium is a single column and not the whole block. Exam tip: s-block is groups 1 and 2, d-block is groups 3 to 12, p-block is groups 13 to 18.

The correct answer is A, Papaya. A unisexual flower carries only one kind of reproductive organ, either stamens or a pistil, while a bisexual flower carries both. Papaya is dioecious: male and female flowers are borne on separate plants, so pollen must travel from a male tree to a female tree before fruit can set, which is why growers keep a few male trees in a papaya orchard. Other familiar unisexual examples are maize, cucumber, watermelon and coconut, in which the two kinds of flower sit on the same plant and the plant is called monoecious. Option B is wrong because the disc florets of a sunflower head are bisexual. Option C is wrong because the hibiscus flower is a standard bisexual flower carrying both stamens and a pistil. Option D is wrong because mustard, a member of the family Brassicaceae, also bears bisexual flowers. Exam tip: unisexual flowers include papaya, maize, cucumber and watermelon, while hibiscus, mustard, rose and pea are bisexual.

The correct answer is D. Ionic compounds dissolve well in water but not in kerosene, petrol or other non-polar organic solvents, so this statement is not a property of theirs. The reason is that ionic compounds are made of positive and negative ions held together by strong electrostatic force, and only a polar solvent such as water can pull those ions apart by surrounding them. Kerosene and petrol are non-polar and cannot do this. A is a true property, because the strong force between ions needs a lot of heat to break, giving sodium chloride a melting point of about 801 degrees Celsius. B is true, as the rigid lattice of ions makes these compounds hard, brittle solids at room temperature. C is true, because ions become free to move once the solid is melted or dissolved in water, and then they carry current. Exam tip: ionic compounds are water-soluble and conduct only when molten or in solution.

The correct answer is C, To increase friction. The grooves cut into a sole grip the ground, so the foot does not slip while walking or running. Friction is the force that acts between two surfaces in contact and opposes motion between them. It becomes larger when the surfaces are rough, which is why the tread of a sole, the grooves of a tyre and the ridges of a bicycle handle are all made rough on purpose. A smooth sole on a wet floor has very little friction, and that is why people slip there. The same rubbing slowly wears the tread away, so an old shoe or tyre grips poorly and has to be replaced. A is wrong because a sole protects the foot by its thickness and material, not by its pattern. B is wrong because less friction would make walking unsafe; oil and ball bearings are used where friction has to be reduced. D is wrong because treading does not lengthen the life of a shoe. Exam tip: rough surface means more friction – treads, grooves and studs are all made to grip.

The correct answer is A, 5, 10 and 2 respectively. Copper sulphate holds five water molecules, sodium carbonate ten and gypsum two, so the order asked for is 5, 10 and 2. Water of crystallisation is the fixed number of water molecules joined to one formula unit of a salt, and it is written after a dot in the formula. Copper sulphate is CuSO4.5H2O, the blue vitriol that turns white on heating and blue again when water is added to it. Sodium carbonate is Na2CO3.10H2O, the washing soda of everyday use, and gypsum is CaSO4.2H2O, which on partial heating gives plaster of Paris. B is wrong because it swaps the figures for copper sulphate and sodium carbonate. C is wrong because it gives sodium carbonate two and gypsum ten. D is wrong because it leaves copper sulphate with only two water molecules. Exam tip: learn the trio together, blue vitriol 5, washing soda 10 and gypsum 2.

The correct answer is A, Capra aegagrus hircus. The domestic goat is treated as a subspecies of the wild goat, so its name carries three parts — the genus Capra, the species aegagrus and the subspecies hircus. It is often shortened to Capra hircus. Carl Linnaeus gave science this binomial system, in which the genus name begins with a capital letter, the species name does not, and the whole name is printed in italics or underlined when handwritten. Goats were among the first animals humans tamed, in western Asia roughly ten thousand years ago, and India keeps one of the largest goat populations in the world. Option B is wrong because Bos indicus is the humped Indian cattle, the zebu. Option C is wrong because Sus scrofa is the wild boar, the ancestor of the domestic pig. Option D is wrong because Ovis aries is the domestic sheep, the animal most often confused with the goat in such questions. Exam tip: goat Capra hircus, sheep Ovis aries, cattle Bos indicus, buffalo Bubalus bubalis.

The correct answer is C, the carboxyl group. Ethanoic acid, better known as acetic acid and familiar as vinegar in dilute form, has the formula CH3COOH, and the -COOH group at the end is what makes it acidic, since it releases a hydrogen ion in water and turns blue litmus red. Option A is wrong because the hydroxyl group marks an alcohol such as ethanol, C2H5OH, which is neutral to litmus. Option B is wrong because the aldehyde group ends in -CHO, as in ethanal, and an aldehyde is easily oxidised to the corresponding acid but is not itself acidic. Option D is wrong because the ketone group lies between two carbon atoms, as in propanone or acetone, and is likewise not acidic. A useful pair to remember is that ethanol oxidises to ethanoic acid.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is D, carbohydrates. A dilute solution of iodine gives a deep blue-black colour with starch, which is a polysaccharide and therefore a carbohydrate. The colour appears because iodine molecules slip into the coiled amylose chains of starch, and the test is used on rice, potato and bread in school laboratories and in food testing.

Option A is wrong because cholesterol is detected by the Liebermann-Burchard or Salkowski reaction, not by iodine. Option B is wrong because fat is shown by the translucent spot test on paper or by Sudan III staining. Option C is wrong because protein is detected by the biuret test, which gives a violet colour, or by the ninhydrin test. Iodine belongs only with starch, and that is the pairing to remember.

Remember also that iodine itself is an element, and the blue-black colour disappears on heating and returns on cooling.

The correct answer is C, a mechanism to reduce CO2 emission. A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions. The heat of fission is produced in the reactor core, carried away by a coolant, passed to water in a heat exchanger or steam generator, and the steam then turns a turbine coupled to a generator. Control rods of cadmium or boron absorb spare neutrons and a moderator such as heavy water slows them down so that fission continues steadily. Option A is wrong as a choice because the turbine is the part that actually converts steam energy into electricity. Option B is wrong because the heat exchanger carries heat from the radioactive coolant loop to the clean water loop. Option D is wrong because the reaction chamber, the core holding the fuel rods, is where fission happens. Exam tip: a nuclear plant emits no carbon dioxide; its waste problem is spent radioactive fuel instead.

The correct answer is B, mitochondria and plastids. Both carry a small circular DNA of their own and their own 70S ribosomes, so they make a part of their protein themselves and divide independently of the cell; this semi-autonomous nature is the main evidence for the view that they descend from free-living bacteria engulfed by an early cell. Option A is wrong because the Golgi body and the endoplasmic reticulum are membrane systems that modify and transport material and carry no genetic matter of their own; the rough endoplasmic reticulum merely holds ribosomes on its outer surface. Option C is wrong because the lysosome is only a sac of digestive enzymes and the Golgi body, as stated, has no DNA. Option D is wrong because the vacuole is a storage sac bounded by the tonoplast and has no DNA, even though its partner in the option, the plastid, does. Remember the pair as the two power organelles of the cell.

The correct answer is A, Used on ordinary combustibles such as wood and paper. Fires are sorted into classes by what is burning, and Class A covers ordinary solid fuels — wood, paper, cloth, straw, rubber and many plastics. These fires leave glowing embers, so they are put out mainly by cooling, and plain water or a water-based extinguisher is the cheapest and most effective choice for them. Option B is wrong because burning liquids such as petrol, kerosene, oil, paint and solvents are Class B, where water would spread the fire and foam or dry powder is used instead. Option C is wrong because a fire in live electrical equipment is a separate class — Class C in the American scheme and marked Class E in the Indian and European ones — and it needs a non-conducting agent such as carbon dioxide, never water. Option D is wrong because burning metals such as magnesium, sodium and potassium form Class D and need a special dry powder, since water reacts violently with them. Exam tip: A — solids, B — liquids, C — gases, D — metals, F or K — cooking oil.

The correct answer is A, 42 degrees Celsius. A clinical thermometer is marked from 35 to 42 degrees Celsius, which on the Fahrenheit scale is 94 to 108 degrees. The scale is kept short because human body temperature never strays far from the normal value of about 37 degrees Celsius, or 98.6 degrees Fahrenheit, and a narrow range lets the marks be spaced widely enough to read a change of one tenth of a degree. The mercury type has a kink, a narrow bend just above the bulb, which stops the mercury from running back so the reading can be taken after the thermometer is removed. B, C and D are wrong because temperatures of 44, 46 and 48 degrees Celsius lie far beyond what a living body can reach, so those markings would be wasted; a laboratory thermometer covering about minus 10 to 110 degrees Celsius is used for such higher readings. Exam tip: clinical 35 to 42 degrees Celsius, normal body temperature 37 degrees Celsius.

The correct answer is A, 250 cm. In an astronomical telescope set for normal adjustment, the magnifying power equals the focal length of the objective divided by the focal length of the eyepiece. Here the magnification is 100 and the eyepiece is 2.5 cm, so the objective must be 100 multiplied by 2.5, that is 250 cm. This is why astronomical telescopes are long instruments: a large objective focal length with a short eyepiece focal length gives high magnification, and in normal adjustment the tube length is roughly the sum of the two focal lengths. B is wrong because an objective of 40 cm would give a magnification of only 16. C is wrong because a focal length smaller than the eyepiece would shrink the image instead of enlarging it. D is wrong because 100 cm gives a magnification of 40. Exam tip: for a telescope magnification is objective divided by eyepiece, so the objective is the longer lens.

The correct answer is A, Deposition. Deposition is the direct change of a substance from the gaseous state to the solid state, without passing through the liquid state in between. It is the exact reverse of sublimation. Frost forming on a cold window pane on a winter morning is deposition, because water vapour in the air turns straight into ice crystals. Iodine vapour and carbon dioxide behave the same way when they are cooled strongly. In such a change the particles lose energy, come very close together and settle into a fixed arrangement, so the substance gets a definite shape and volume. B is wrong because sublimation is the opposite change, a solid turning directly into a gas, as camphor and naphthalene balls do. C is wrong because vaporisation is a liquid changing into a gas. D is wrong because freezing is a liquid changing into a solid, as water does at 0 degree Celsius. Exam tip: remember the pair, sublimation is solid to gas and deposition is gas to solid.

The correct answer is D, 11.36%. Mass by mass percentage of a solution is the mass of the solute divided by the mass of the whole solution, multiplied by 100. The solute here is 41 g of common salt and the solvent is 320 g of water, so the mass of the solution is 41 plus 320, that is 361 g. The concentration is therefore 41 divided by 361, multiplied by 100, which gives 11.36 per cent. The common mistake is to divide by the mass of the solvent alone instead of the solution; 41 divided by 320 into 100 gives 12.81 per cent, which is not even an option. A is wrong because 12.36 per cent would need about 45 g of salt in the same solution. B is wrong because 9.35 per cent would need about 34 g of salt. C is wrong because 10.36 per cent would need about 37 g of salt. Exam tip: mass percentage always uses solute divided by solute plus solvent, never solute divided by solvent.

The correct answer is B, Class B. Fires are sorted into classes by what is burning, and a fire fed by flammable liquids such as petrol, diesel, kerosene, oil, paint or thinner is a class B fire. Such a fire is put out by smothering it with foam, carbon dioxide or dry chemical powder, which cuts off the oxygen. Water must never be thrown on burning oil, because the liquid floats on water and spreads the flames further. A is wrong because class D fires involve burning metals like magnesium, sodium and potassium, which need special dry powders. C is wrong because class C covers fires in live electrical equipment in common usage, and flammable gases under the Indian Standard. D is wrong because class A fires are the ordinary ones in solids like wood, paper and cloth, where water is the cheapest and best agent. Exam tip: A for solids, B for liquids, C for electrical or gas and D for metals.

The correct answer is A, low coefficient of friction. Teflon is the trade name of polytetrafluoroethylene, a polymer whose surface is one of the most slippery among solids, with a coefficient of friction of about 0.04. A bearing has to let a shaft turn with as little rubbing as possible, so this slipperiness is the reason Teflon is chosen; it also lets many such bearings work without any oil or grease. The polymer was found by accident by Roy Plunkett in 1938, resists almost every chemical and holds up to about 260 degrees Celsius, which is why it also coats non-stick cookware and is wound as sealing tape on pipe threads. B is wrong because Teflon is a poor conductor of heat, so it is not chosen to carry heat away. C is wrong because saving space depends on the design of the bearing, not on the material. D is wrong because only the first reason holds. Exam tip: Teflon is PTFE, the non-stick polymer with the lowest friction.