General Science Mixed Quiz: Set 46

The correct answer is D, nickel. An alkene has a carbon-carbon double bond, and adding hydrogen across that bond turns it into the corresponding alkane. The reaction needs a finely divided metal catalyst, and nickel is the cheap industrial choice, usually at about 150 to 200 degrees Celsius; palladium and platinum do the same job at lower temperatures. The catalyst holds hydrogen molecules on its surface, splits them into atoms and lets them join the double bond, so it only speeds the reaction up and is not used up. The best known use is in food: unsaturated vegetable oils are hydrogenated over nickel to make solid vanaspati ghee. Option A is wrong because copper is used to dehydrogenate alcohols, which is the opposite kind of change. Option B is wrong because zinc dust is used for other reductions, not for adding hydrogen to a double bond. Option C is wrong because aluminium is not a hydrogenation catalyst at all. Exam tip: alkene plus hydrogen over nickel gives an alkane; oil plus hydrogen over nickel gives vanaspati.

The correct answer is C, Avogadro. The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811. It says that equal volumes of all gases at the same temperature and pressure hold the same number of molecules, so the volume of a gas is directly proportional to the number of moles in it. This is why one mole of any gas occupies 22.4 litres at standard temperature and pressure, and why the number of particles in one mole, about 6.022 x 10 to the power 23, is named the Avogadro number after him. A is wrong because Charles law links the volume of a fixed mass of gas to its temperature at constant pressure. B is wrong because Boyle's law says that volume varies inversely with pressure at constant temperature. D is wrong because Gay-Lussac gave the law of combining volumes and the pressure-temperature law. Exam tip: Avogadro ties volume to the number of molecules, Boyle to pressure and Charles to temperature.

The correct answer is C, salivary amylase, also called ptyalin. It is secreted by the three pairs of salivary glands and breaks starch into the smaller sugar maltose, which is why starch is the only class of food whose digestion actually begins in the buccal cavity. Option A is wrong because pepsin is secreted by the gastric glands of the stomach and works only on protein, and only in a strongly acidic medium. Option B is wrong because trypsin comes from the pancreas, acts in the duodenum and also digests protein, not starch. Option D is wrong because lipase, again from the pancreas, acts on fat that bile has already emulsified, and breaks it into fatty acids and glycerol. Note that a long chew makes bread taste sweet, which is the everyday proof that salivary amylase is turning starch into sugar.

The correct answer is C, Stomata. Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them. Each stoma is bounded by two bean-shaped guard cells that swell to open the pore and shrink to close it, and this is how the plant controls its water loss. Most stomata lie on the lower surface of a leaf, so less water is lost to direct sunlight. Transpiration also happens largely through these pores. A is wrong because the cell membrane controls what enters and leaves a single cell, not the gas exchange of the whole plant. B is wrong because the nucleus carries the genetic material and directs the activities of the cell. D is wrong because guard cells only open and close the pore, while the exchange itself happens through the stomatal opening. Exam tip: stomata do the gas exchange and transpiration, guard cells only open and close them.

The correct answer is D, group O. In the ABO system the antigens sit on the surface of the red blood cell and the antibodies float in the plasma. Group O red cells carry neither the A antigen nor the B antigen, so there is nothing on them for the recipient's antibodies to attack, and blood of this group can be given to a person of any ABO group. That is why group O is called the universal donor. Option A is wrong because group A cells carry the A antigen and would be destroyed by the anti-A antibody present in the plasma of groups B and O. Option B is wrong for the same reason with the B antigen. Option C is wrong because group AB is the opposite case: its plasma has no anti-A or anti-B antibody, so it can receive from everyone and is called the universal recipient, not the universal donor. Keep the pair straight: O gives to all, AB takes from all.

The correct answer is D, Colourless. Hydrogen is a colourless, odourless and tasteless gas, so none of the colours listed fits it. It is the lightest element, with one proton and one electron, and it is the most abundant element in the universe, although on the earth it is found mostly combined in water and in organic compounds. Hydrogen exists as the diatomic molecule H2, burns in air with a pale blue flame and gives only water as the product, which is why it is studied as a clean fuel. It is used to make ammonia by the Haber process and to harden vegetable oils into vanaspati. A is wrong because no common form of hydrogen is yellow. B is wrong because orange is the colour seen in sodium vapour lamps and not in hydrogen. C is wrong because none of the gases here is black; carbon in its soot form is black, but that is a solid. Exam tip: hydrogen, oxygen and nitrogen are all colourless and odourless gases.

The correct answer is B, AgBr. Silver bromide is the standard example of an ionic crystal that carries both kinds of point defect at the same time. A Schottky defect is a missing pair, one cation vacancy with one anion vacancy, so the crystal stays electrically neutral but loses mass and its density falls; it appears where the two ions are close in size and the coordination number is high. A Frenkel defect is the smaller ion, usually the cation, slipping out of its lattice site into an interstitial space, so the mass and the density are unchanged; it appears where the two ions differ widely in size. In silver bromide the small silver ion can move into an interstitial hole while vacancy pairs also form, so both defects are seen. A is wrong because AgF, whose ions are comparable in size, shows only the Schottky defect. C is wrong because AgCl shows the Frenkel defect. D is wrong because NaCl is the classic Schottky example. Exam tip: a Schottky defect lowers density, a Frenkel defect does not, and AgBr shows both.

The correct answer is B, In the same direction. In a class 3 lever the fulcrum is at one end, the effort is applied in the middle and the load sits at the far end. Since both the effort and the load lie on the same side of the fulcrum, the beam turns one way and they move in the same direction. The effort arm is shorter than the load arm, so the mechanical advantage is less than one and more effort is needed than the load; what such a lever gains is speed and a wider sweep of movement. The human forearm, a pair of sugar tongs, a fishing rod and a stapler work this way. A is wrong because effort and load move oppositely in a class 1 lever, where the fulcrum lies between them, as in a see-saw or scissors. C is wrong because a lever turns about a fixed point and its two ends never move at right angles to each other. D is wrong because the size of the load changes the force needed, not the direction of motion. Exam tip: class 1 has the fulcrum in the middle, class 2 the load, class 3 the effort.

The correct answer is C, Platyhelminthes. Flatworms, the phylum Platyhelminthes, have an incomplete digestive system with just one opening, so the same mouth takes the food in and throws the waste out. Their gut is a blind sac with no anus. Planaria, the liver fluke and the tapeworm belong here, and the tapeworm has no gut at all, absorbing food through its body wall. Flatworms are triploblastic, acoelomate and bilaterally symmetrical, and many of them are parasites. A complete digestive system, with a separate mouth and anus, appears from the roundworms onwards. A is wrong because arachnids such as spiders and scorpions are arthropods and have a complete gut. B is wrong because echinoderms like the starfish and sea urchin have both a mouth and an anus. D is wrong because arthropods, the largest phylum of the animal kingdom, have a complete alimentary canal. Exam tip: Coelenterata and Platyhelminthes have a single opening; from Aschelminthes onwards the gut has two.

The correct answer is C, 1.6 sec. Time period is the time taken for one full oscillation, so it is the total time divided by the number of oscillations: 64 divided by 40 gives 1.6 seconds. Frequency is the reverse quantity, the number of oscillations in one second, which here is 40 divided by 64, or 0.625 hertz; period and frequency are always reciprocals of each other. For a simple pendulum the period depends only on the length of the thread and on the acceleration due to gravity, through T equal to 2 pi times the square root of L by g. It does not depend on the mass of the bob, nor, for small swings, on how wide the swing is. A pendulum about one metre long has a period of close to two seconds. A is wrong because 0.6 second would give more than 100 oscillations in 64 seconds. B and D are wrong because 6 and 16 seconds are far too long for 40 swings in just over a minute. Exam tip: time period equals total time divided by the number of oscillations.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is B, are long chain molecules held together by secondary bonds. In a thermoplastic the polymer exists as long linear or lightly branched chains, and one chain is held to the next only by weak secondary forces such as van der Waals attraction. Heat gives enough energy to loosen those weak links, so the material softens, can be moulded into a new shape and hardens again on cooling, and the cycle can be repeated, which is why thermoplastic waste is recyclable. Polyethylene, polypropylene, PVC, polystyrene and nylon all belong to this group. A is wrong because a three-dimensional network of strong primary bonds describes a thermosetting plastic such as bakelite, which sets once and cannot be remoulded. C is wrong because the ability to deform plastically rises with temperature instead of falling. D is wrong because the secondary bonds do break as thermal energy rises, and that is exactly why the plastic softens. Exam tip: thermoplastic means weak secondary bonds and remoulding, thermosetting means cross-linked primary bonds and a shape set for good.

The correct answer is D, Neon. When electricity is passed through a sealed tube holding neon at low pressure, the gas atoms are excited and give out a bright orange-red glow, which is why advertising signs are still called neon signs. Neon is a noble gas discovered in 1898 by Ramsay and Travers; it is chemically inert, forms no ordinary compounds, and is also used in voltage testers, high-voltage indicators and lightning arresters. Every gas glows in its own colour in a discharge tube, and that colour is the fingerprint of its atomic energy levels. Option A is wrong because helium gives a pale pinkish-white glow and is better known for filling balloons and airships. Option B is wrong because argon glows a pale violet-blue and is used to fill electric bulbs and to shield welding. Option C is wrong because nitrogen glows bluish, and its common uses are as an inert packing gas and as a liquid coolant. Exam tip: neon gives red light in a discharge tube, while argon is the gas that fills ordinary electric bulbs.

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 C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is B, Static friction > Kinetic friction > Rolling friction. For the same pair of surfaces the order of friction is always static, then kinetic, then rolling. Static friction is the largest because the surfaces interlock while at rest and that grip has to be broken to start motion. Once sliding begins the contact keeps breaking and remaking, so kinetic friction is smaller. Rolling friction is the smallest of the three, since a rolling wheel does not slide over the road but only presses and deforms it slightly at the point of contact. This is exactly why wheels, rollers and ball bearings are used to shift heavy loads. A and D are wrong because they place rolling friction at the top, though it is the least of the three. C is wrong because it puts rolling friction above kinetic friction, reversing the true order. Exam tip: static greater than kinetic greater than rolling; the smallest of them gave us the wheel.

The correct answer is B, 1.5055 × 10²³. One mole of any gas occupies 22.4 litres at STP, so 5.6 litres is 5.6 divided by 22.4, that is one quarter of a mole. A mole contains 6.022 × 10²³ particles, the Avogadro number, so a quarter of a mole of oxygen contains 6.022 × 10²³ divided by four, which works out to 1.5055 × 10²³ molecules. Note that the question asks for molecules; since oxygen is diatomic, the number of atoms would be twice this figure. Option A is wrong because 6.022 × 10²³ is the count for a full mole, that is for 22.4 litres. Option C is wrong because 2.24 × 10²³ comes from confusing the molar volume 22.4 with the particle count. Option D is wrong because 3.011 × 10²³ is half a mole, which would be 11.2 litres. Exam tip: at STP, 22.4 litres equals one mole equals 6.022 × 10²³ molecules, so divide the given volume by 22.4 first.

The correct answer is B, there is incomplete combustion. Naphthalene is an aromatic hydrocarbon, C10H8, with a very high proportion of carbon, so the air around the flame cannot supply enough oxygen to burn all of it to carbon dioxide. The unburnt carbon leaves the flame as glowing soot particles, which is what makes the light yellow and the smoke black. This is the general rule for unsaturated and aromatic compounds, while saturated hydrocarbons burn with a clean blue flame. The same chemistry explains why a kerosene lamp smokes and why the air holes of a gas burner are opened to get a blue flame. Option A is wrong because the carbon to hydrogen ratio in naphthalene is high, not low, and that is precisely the cause. Option C is wrong because excess air would give complete combustion and a clean flame. Option D is wrong because sooty burning comes from carbon itself, not from nitrogen or sulphur impurities. Exam tip: saturated compounds give a blue flame, unsaturated and aromatic ones a yellow sooty flame.

The correct answer is B. Bile is made in the liver, stored and concentrated in the gall bladder and poured into the duodenum, and it carries bile salts and bile pigments but not a single digestive enzyme. Its bile salts break the large globules of fat into very fine droplets, a process called emulsification, which multiplies the surface on which pancreatic lipase can act, and it also neutralises the acid arriving from the stomach so that the alkaline pancreatic and intestinal enzymes can work. Option A is wrong because that chemical breakdown is the work of lipase, not of bile. Option C is wrong because absorption through the villi is a separate step that follows digestion and is not performed by bile. Option D is wrong because no secretion of the body converts fat into starch; the two are different classes of nutrient.

The correct answer is B, the sino-atrial node. The heartbeat is not started by a nerve from the brain; the heart generates its own rhythm, and the patch of specialised tissue that does so fastest sets the pace for the rest. That patch is the sino-atrial node, lying in the wall of the right atrium near the opening of the superior vena cava, and it is therefore called the pacemaker of the heart. Option A is wrong because the atrio-ventricular node only receives the impulse from the sino-atrial node and delays it briefly so that the atria can finish emptying; it can take over as a slower backup pacemaker but is not the normal one. Option C is wrong because the bundle of His is the conducting pathway that carries the impulse from the atrio-ventricular node into the septum between the ventricles. Option D is wrong because the Purkinje fibres are the final branches that spread the impulse through the ventricular muscle. The order to memorise is sino-atrial node, atrio-ventricular node, bundle of His, Purkinje fibres.