General Science Mixed Quiz: Set 42

The correct answer is B, CnH2n+2. Alkanes are saturated hydrocarbons in which carbon atoms are joined only by single bonds, and such a chain carries the largest possible number of hydrogen atoms, given by CnH2n+2. Putting n equal to 1 gives CH4, methane; n equal to 2 gives C2H6, ethane; and n equal to 3 gives C3H8, propane. Because every carbon already holds as much hydrogen as it can, alkanes are unreactive towards addition and are also called paraffins. A is wrong because CnH2n-2 is the formula of alkynes, which contain a triple bond, such as ethyne C2H2. C is wrong because CnH3n-3 belongs to no homologous series of hydrocarbons. D is wrong because CnH2n is the formula of alkenes, which contain one double bond, such as ethene C2H4. Exam tip: learn the three together - alkane CnH2n+2, alkene CnH2n, alkyne CnH2n-2.

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 B, 3 : 1. Aqua regia is a freshly prepared mixture of three parts concentrated hydrochloric acid to one part concentrated nitric acid. Neither acid alone attacks gold, but together they do, because the nitric acid oxidises the metal while the chloride ions hold the gold in solution as a complex. It is used to refine and test gold and platinum.

Option A is wrong because it reverses the proportion and would leave too little hydrochloric acid to form the complex. Option C is wrong because an equal mixture is not the recognised composition. Option D is wrong because no standard preparation uses two to three. The name itself is a clue: aqua regia means royal water, since it dissolves the royal metals, while aqua fortis, or strong water, is nitric acid alone.

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, nerve cell. A neuron carries a long process called an axon, which in a human being may run from the base of the spine to the toe, so a single nerve cell can be about a metre long; this length lets one cell carry an impulse over a great distance without any relay. Option A is wrong because the red blood cell is a small biconcave disc of a few micrometres, and in mature form it has no nucleus at all, which leaves more room for haemoglobin. Option B is wrong because a skeletal muscle fibre is indeed long and multinucleate, but shorter than the longest neuron, and it is the second choice examiners place as a distractor. Option D is wrong because a bone cell, the osteocyte, sits in a small cavity called a lacuna and is compact. Two companion facts are worth carrying: the smallest cell known is Mycoplasma and the largest single cell is the egg of an ostrich.

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 D, Wood, Air, Sand. All three are mixtures: wood is made of cellulose, lignin, water and resins, air is a mixture of nitrogen, oxygen and other gases, and sand is mostly silica mixed with mineral and shell grains. A mixture holds two or more substances that keep their own properties and are not joined in any fixed ratio, so its parts can be separated by physical means such as filtering or sieving. A compound, in contrast, is formed when elements combine chemically in a fixed proportion and shows new properties of its own. A and C are wrong because water is a compound, with hydrogen and oxygen chemically joined in the fixed ratio of two to one. B and C are wrong because common salt is also a compound, sodium chloride, with sodium and chlorine in a fixed ratio. Exam tip: air, wood, sand, milk and sea water are mixtures, while water, common salt, sugar and carbon dioxide are compounds.

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 B, 111 u. Calcium chloride is an ionic compound, so it has a formula unit mass rather than a molecular mass, and the value is found by adding the atomic masses of all the atoms in the formula. Calcium has an atomic mass of 40 u and chlorine of 35.5 u, and the formula carries two chlorine atoms, so the sum is 40 plus 2 multiplied by 35.5, that is 40 plus 71, which gives 111 u. The half unit in chlorine comes from its two isotopes, chlorine-35 and chlorine-37, mixed in roughly a three to one ratio, and forgetting that 0.5 is the usual slip in this sum. A is wrong because 105 u would follow from taking chlorine as 32.5 u. C is wrong because 121 u would need chlorine at 40.5 u. D is wrong because 100 u comes from rounding chlorine down to 30 u. Exam tip: Ca is 40 u and Cl is 35.5 u, so CaCl2 is 111 u while NaCl is 58.5 u.

The correct answer is C, C-12. Relative atomic mass is measured against the carbon-12 atom, one-twelfth of whose mass is taken as the standard unit. That unit is the atomic mass unit, written u, and it is defined as exactly one-twelfth of the mass of one atom of carbon-12. So when we say the relative atomic mass of oxygen is 16 u, we mean one oxygen atom is sixteen times as heavy as one-twelfth of a carbon-12 atom. The International Union of Pure and Applied Chemistry fixed carbon-12 as the standard in 1961 because it gave the most consistent values. A is wrong because nitrogen-14 was never used as the standard. B is wrong because oxygen-16 was the older standard, replaced by carbon-12. D is wrong because C-16 is not even a known isotope of carbon used here. Exam tip: 1 u equals one-twelfth the mass of a carbon-12 atom.

The correct answer is D, CnH2n. An alkene carries one carbon-to-carbon double bond, and that bond uses up two hydrogen atoms that a saturated chain would have held, so the formula drops from CnH2n+2 to CnH2n. Putting n equal to 2 gives C2H4, ethene, the simplest alkene; n equal to 3 gives C3H6, propene. There is no alkene with a single carbon, because a double bond needs two carbon atoms. Being unsaturated, alkenes readily take part in addition reactions, which is how ethene is turned into polythene and how vegetable oils are hardened. A is wrong because CnH2n+2 is the alkane formula. B and C are wrong because CnH2n-1 and CnH2n+1 describe radicals or groups, not stable hydrocarbon series; CnH2n+1 is the alkyl group. Exam tip: each double bond removes two hydrogen atoms, so alkene is CnH2n.

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, lactic acid. When milk is set into curd, the bacteria Lactobacillus convert the milk sugar lactose into lactic acid, and it is this acid that gives curd its sour taste and makes the milk protein clot. The same acid accumulates in muscles during heavy exercise when oxygen supply is insufficient.

Option A is wrong because citric acid is found in lemon, orange and other citrus fruits. Option C is wrong because tartaric acid is found in tamarind and in grapes, and is also a component of baking powder along with baking soda. Option D is wrong because oxalic acid is found in tomato, spinach and sorrel, and is the acid whose calcium salt can form kidney stones. The pairing of each food with one acid is what examiners test.

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 A, cardiac muscle. The muscle of the heart shows light and dark bands under the microscope, so it is striated, yet it is not under the control of the will and it contracts rhythmically without rest for the whole of life, so it is involuntary; this unusual combination is exactly why it is asked. Option B is wrong because skeletal muscle is striated but voluntary, moving when the person wills it. Option C is wrong because smooth or unstriated muscle, found in the walls of the alimentary canal, blood vessels and urinary bladder, has no bands and is involuntary, so it fails the striated half of the question. Option D is wrong because the biceps is a named skeletal muscle of the arm and is therefore voluntary. Remember the three-line table: skeletal, striated and voluntary; smooth, unstriated and involuntary; cardiac, striated and involuntary.

The correct answer is D, Gustatory receptors. The receptors that pick up taste are called gustatory receptors, and they sit inside the taste buds on the tongue. They respond only to substances dissolved in saliva, which is why a dry tongue tastes little, and they report five basic tastes, sweet, sour, salty, bitter and umami. From the tongue the signal travels along cranial nerves to the brain, where taste and smell together give food its flavour. A is wrong because sensory receptor is the broad name for every receptor of the body, including those for light, sound, touch and pressure. B is wrong because chemoreceptor is the wider class that covers both taste and smell, so it does not name the taste receptor in particular. C is wrong because olfactory receptors lie in the lining of the nose and detect smell. Exam tip: gustatory means taste, olfactory means smell, auditory means hearing.

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 A, CnH2n+2. Alkanes are saturated hydrocarbons, so every bond between two carbon atoms is a single bond and all the remaining valencies are filled by hydrogen. Carbon is tetravalent, so a chain of n carbon atoms can hold 2n+2 hydrogen atoms once the two ends of the chain are capped: methane is CH4, ethane C2H6, propane C3H8 and butane C4H10, each member differing from the next by one CH2 unit. Because the carbon skeleton is already saturated, alkanes give substitution reactions rather than addition reactions, and they burn with a clean blue flame, which is why they serve as household and industrial fuels. B is wrong because CnHn+1 fits no hydrocarbon series at all. C is wrong because CnH2n-1 is not a saturated formula either; the alkyne series follows CnH2n-2. D is wrong because CnH2an+1 is a garbled form; it is the alkyl groups, not the alkanes, that follow CnH2n+1. Exam tip: alkane CnH2n+2, alkene CnH2n, alkyne CnH2n-2.

The correct answer is B, sodium hydrogen carbonate. In a soda-acid extinguisher a solution of sodium hydrogen carbonate is kept in the body of the cylinder and sulphuric acid in a sealed glass phial. When the knob is struck the phial breaks, the acid meets the bicarbonate and a large volume of carbon dioxide is produced. The gas drives the water out of the nozzle and also blankets the fire, cutting off oxygen.

Option A is wrong because sodium chloride does not react with sulphuric acid to give a gas that puts out fire. Option C is wrong because calcium oxide reacts with water giving off heat, which would make matters worse. Option D is wrong because potassium nitrate is an oxidising agent used in gunpowder and would feed a fire rather than stop it.

The correct answer is B, blood. Blood is classed as a connective tissue because its cells lie in a matrix, and because that matrix, the plasma, is liquid it is called a fluid connective tissue; the red cells, white cells and platelets float in it and it connects the organs of the body by carrying gases, food, wastes and hormones between them. Option A is wrong because cartilage is a connective tissue too, but its matrix is solid and flexible, not fluid. Option C is wrong because epithelium is a covering and lining tissue with its cells packed tightly together and almost no matrix between them. Option D is wrong because nervous tissue is made of neurons specialised to conduct impulses and is a separate one of the four animal tissue types. Lymph is the second fluid connective tissue and is the usual second option in a two-statement version of this question.