General Science Mixed Quiz: Set 44

The correct answer is D, Radiation. Radiation carries heat as electromagnetic waves, so it needs no material medium and can travel through a vacuum. This is how the heat of the Sun crosses empty space to reach the Earth, and why you feel warmth in front of a fire without touching it. Every body above absolute zero radiates energy, and the hotter the body, the more it radiates. A is wrong because it pairs radiation with conduction, and conduction cannot work without a medium. B is wrong because in conduction heat passes from particle to particle inside a solid, so a material medium is essential. C is wrong because convection works through the bulk movement of a heated liquid or gas, so it too needs a medium and stops in a vacuum. Exam tip: conduction needs a solid, convection needs a fluid, radiation needs nothing - only radiation crosses a vacuum.

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 D, f. The focal length of a mirror does not depend on the medium around it, so a convex mirror of focal length f in air keeps the focal length f inside the liquid. A mirror works by reflection, and for a spherical mirror f = R/2, where R is the radius of curvature of its surface. R is fixed by the shape of the mirror alone, so replacing air with water, oil or any other liquid changes nothing. A lens is the opposite case, because it works by refraction: its focal length depends on the refractive index of the glass relative to the medium around it, so a lens does change its focal length in a liquid. A is wrong because multiplying f by 4/3 treats the mirror as if it were a lens. B is wrong for the same reason, with the factor merely inverted. C is wrong because 7/3 has no basis here at all. Exam tip: mirror focal length is R/2 and stays fixed in every medium, a lens focal length does not.

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 C, 15. Group 15, the nitrogen family, holds nitrogen, phosphorus, arsenic, antimony and bismuth. Only nitrogen and phosphorus are non-metals; arsenic and antimony are metalloids and bismuth is a metal, so the group has exactly two non-metallic elements. The pattern comes from the trend down a group: as the shells increase, the pull of the nucleus on the outer electrons weakens, the atom gives up electrons more easily, and the character shifts from non-metal to metalloid to metal. A is wrong because group 16 has three non-metals, oxygen, sulphur and selenium, with tellurium a metalloid and polonium a metal. B is wrong because group 14 has only one non-metal, carbon, with silicon and germanium metalloids and tin and lead metals. D is wrong because every usable halogen in group 17, from fluorine to iodine, is a non-metal. Exam tip: non-metals per group - 14 has one, 15 has two, 16 has three.

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, Opening of soda bottle. Nothing is oxidised when a soda bottle is opened; the pressure inside simply falls, the dissolved carbon dioxide becomes less soluble and escapes as bubbles. That is a physical change governed by Henry's law, not a chemical reaction, because the carbon dioxide molecules are unchanged. Oxidation, by contrast, means a substance gains oxygen or loses electrons. Option A is wrong because rusting is oxidation: iron reacts with oxygen and moisture to form hydrated iron oxide, the reddish-brown rust. Option C is wrong because rancidity is the oxidation of fats and oils in food, which gives the stale smell and taste, and is slowed by airtight packing, refrigeration, nitrogen flushing or antioxidants. Option D is wrong because combustion is rapid oxidation with heat and light, as when a fuel burns in air. Exam tip: a change is chemical only when a new substance is formed, so dissolving and fizzing are physical while rusting, rancidity and burning are oxidation.

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, Hydrochloric acid. Muriatic acid is the old trade name for hydrochloric acid, the water solution of hydrogen chloride gas, and the name survives in the market for the crude commercial grade used for cleaning metal and masonry. It is a strong mineral acid that makes chlorides, and industry uses it in fertilizers and dyes, in electroplating and pickling of steel, and in the photographic, textile and rubber trades. Dilute hydrochloric acid is also present in human gastric juice, where it helps digestion. A is wrong because perchloric acid is HClO4, a powerful oxidising acid with no such common name. B is wrong because sulphuric acid, H2SO4, was once called oil of vitriol, not muriatic acid. D is wrong because nitric acid, HNO3, carried the old name aqua fortis. Exam tip: learn the old names - muriatic acid is HCl, oil of vitriol is H2SO4 and aqua fortis is HNO3.

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 B, Emerald. Emerald is the deep green variety of the mineral beryl, a beryllium aluminium silicate, so beryllium is part of its very formula. Traces of chromium, and sometimes vanadium, give the stone its green colour. Beryl is the chief ore of beryllium, a light, stiff metal used in X-ray windows, aerospace alloys and nuclear reactors; aquamarine is the pale blue variety of the same mineral. Option A is wrong because topaz is an aluminium silicate carrying fluorine and hydroxyl groups, with no beryllium in it. Option C is wrong because ruby is corundum, that is aluminium oxide, which turns red because of chromium impurity. Option D is wrong because blue sapphire is the same corundum, coloured blue by traces of iron and titanium. So ruby and sapphire are two colours of one mineral, while emerald belongs to a different family altogether. Exam tip: emerald = beryl (beryllium); ruby and sapphire = corundum (aluminium oxide).

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.

The correct answer is B, halo alkane. A haloalkane carries a halogen atom - fluorine, chlorine, bromine or iodine - bonded to a carbon chain, so no oxygen appears in its functional group at all. Chloroethane, C2H5Cl, is a simple example. A functional group is the atom or group of atoms that decides how a carbon compound behaves, and the halogen makes the carbon attached to it slightly positive, which is why haloalkanes are the usual starting point for substitution reactions in organic chemistry. A is wrong because an alcohol carries the hydroxyl group, written as -OH, in which oxygen is the hetero atom. C is wrong because a ketone carries the carbonyl group, -CO-, placed between two carbon atoms, and that group is built on an oxygen atom. D is wrong because a carboxylic acid carries -COOH, which holds two oxygen atoms, the most of the four choices. Exam tip: among the common functional groups only the haloalkanes and the amines are free of oxygen.

The correct answer is C, 64 u. Sulfur dioxide is made of one sulfur atom and two oxygen atoms, so its molecular mass is the sum of their atomic masses: 32 plus 2 multiplied by 16, that is 32 plus 32, which gives 64 u. Molecular mass is expressed in unified atomic mass units, written u, and one u is defined as one-twelfth of the mass of a carbon-12 atom. Sulfur dioxide itself is the pungent, colourless gas released when sulfur or a sulfur-rich fuel such as coal is burnt, and in the atmosphere it is oxidised and dissolves to form sulfuric acid, the chief cause of acid rain. A is wrong because 6.4 u is the correct total divided by ten, a decimal slip. B is wrong because 65 u would need oxygen to weigh 16.5 u. D is wrong because 6.5 u repeats the decimal slip on an already wrong total. Exam tip: S is 32 u and O is 16 u, so SO2 is 64 u while SO3 is 80 u.

The correct answer is B, Emulsification. Mayonnaise is an emulsion: very small droplets of oil are beaten into a watery liquid of egg yolk with vinegar or lemon juice, and the droplets stay spread out instead of separating into a layer. Oil and water do not mix on their own, so such a mixture needs an emulsifying agent, and here it is the lecithin of the egg yolk, whose molecules have one end that likes water and another that likes oil, so they coat each droplet and keep it away from its neighbours. Milk is a natural emulsion of fat in water, and butter is an emulsion of water in fat. Option A is wrong because caramelisation is the browning of sugar on strong heating. Option C is wrong because the Maillard reaction is the browning of a protein with a reducing sugar that gives bread crust and roasted meat their colour. Option D is wrong because oxidation of fat turns it rancid. Exam tip: mayonnaise is oil in water held together by the lecithin of egg yolk, an emulsion.

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 A, Lysosomes. They are called the suicide bags of the cell because they are packed with digestive enzymes that can break down the cell's own material. Lysosomes are small membrane-bound sacs built by the Golgi apparatus, and the hydrolytic enzymes inside them work best in an acidic medium. Their normal job is cleaning up: they digest worn-out organelles and bacteria taken in by the cell. When a cell is injured, starved or ageing, the lysosome membrane breaks and these enzymes digest the cell itself, and that is where the nickname comes from. Option B is wrong because plastids occur only in plant cells and store pigments and food or carry out photosynthesis. Option C is wrong because the endoplasmic reticulum is a network of membranes that makes and carries proteins and fats inside the cell. Option D is wrong because mitochondria release energy as ATP and are called the powerhouse of the cell. Exam tip: lysosome is the suicide bag, mitochondrion the powerhouse and ribosome the protein factory.

The correct answer is A, inhalation. Inhalation, also called inspiration, is the phase of breathing in which the diaphragm flattens and the intercostal muscles pull the ribs up and out, so the chest cavity enlarges, the pressure inside the lungs falls below the pressure of the atmosphere and oxygen rich air rushes in through the nostrils and the windpipe. Option B is wrong because exhalation is the opposite phase, in which the muscles relax, the chest cavity shrinks and carbon dioxide rich air is pushed out; it is normally a passive process. Option C is wrong because flotation is a physical property of bodies in a fluid, described by the law of Archimedes, and has nothing to do with breathing. Option D is wrong because exploration simply means searching or investigating and is not a term of biology at all. Remember the pair as inhalation for taking air in and exhalation for sending it out.

The correct answer is B, nephrons. The nephron is the structural and functional unit of the kidney, and each human kidney holds about one million of them. Blood is pushed into the cup shaped Bowman's capsule through a knot of capillaries called the glomerulus, and there the actual filtration happens: water, salts, glucose, amino acids and urea pass out while blood cells and large plasma proteins are held back. Option A is wrong because the ureter is only the tube that carries formed urine from the kidney down to the urinary bladder; it filters nothing. Option C is wrong because neurons are nerve cells that conduct impulses and belong to the nervous system, not the excretory system; the similar sound of nephron and neuron is exactly the trap in this question. Option D is wrong because the urethra is the last passage through which urine leaves the body. Remember the order: nephron filters, ureter carries, bladder stores, urethra releases.

The correct answer is B, 8. The B complex is a group of eight water soluble vitamins that work mainly as helpers in the reactions that release energy from food. They are B1 thiamine, B2 riboflavin, B3 niacin, B5 pantothenic acid, B6 pyridoxine, B7 biotin, B9 folic acid and B12 cyanocobalamin. They were first taken to be one substance and were separated later, which is why the numbers have gaps. Being water soluble, they are not stored in the body for long and must come from the diet, so a shortage shows up quickly as beriberi from B1, pellagra from B3 or anaemia from B12. A, C and D are wrong because six, seven and five fall short of the group, which is complete only at eight members. Exam tip: the B complex has eight vitamins, and B12 is the one that holds cobalt.