General Science Mixed Quiz: Set 35

The correct answer is B, mercury. Mercury is the only metal that is liquid at ordinary room temperature, which is why it was long used in thermometers and barometers; it is also the metal that forms amalgams, alloys in which mercury is one component. Option A, sodium, is a solid, although a very soft one that can be cut with a knife and must be stored under kerosene because it reacts violently with air and water. Option C, lead, is a soft, dense solid with a low melting point, but it is far from liquid at room temperature. Option D, tungsten, has the highest melting point of the metals, which is exactly why it is used for the filament of an incandescent lamp. Among non-metals, bromine is the one that is liquid at room temperature, and gallium and caesium are metals that melt in the warmth of the hand.

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 B, ethyne. An alkyne contains a carbon to carbon triple bond, which needs at least two carbon atoms, so the series begins with ethyne, C2H2, also called acetylene and used with oxygen in welding. Option A is wrong because propyne, with three carbon atoms, is the second member of the series, not the first. Option C is wrong because a compound called methyne cannot exist as an alkyne at all: methane has a single carbon atom and there is no second carbon for it to form a triple bond with, which is exactly the trap the option is meant to spring. Option D is wrong because butyne has four carbon atoms and is the third member. The general formula of the series is CnH2n-2, and putting n equal to two gives C2H2, confirming ethyne as the first member.

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 A, Glucose, Water and Oxygen. Green plants use sunlight trapped by chlorophyll to join carbon dioxide and water, and the balanced equation reads six molecules of carbon dioxide plus twelve of water giving one molecule of glucose, six of oxygen and six of water. Water therefore stands on both sides of the equation: twelve molecules are taken in as raw material and six are released again as a product. The oxygen that is given off comes from splitting water, not from carbon dioxide, a fact proved with heavy oxygen tracers. B is wrong because it drops the water formed during the reaction. C is wrong because starch is not made directly; glucose is the first stable product, and the plant later links glucose units together to store starch. D is wrong for the same reason, since it names starch in place of glucose. Exam tip: glucose first, starch only as storage, and the oxygen comes from water.

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 C, 3:1. Aqua regia is three parts concentrated hydrochloric acid to one part concentrated nitric acid, and the name means royal water, given because the mixture attacks the noble metals gold and platinum, which neither acid can dissolve on its own. Option B, 1:3, is the same pair of acids in the reverse order and is the commonest wrong answer, so note that the larger share is hydrochloric acid. Options A and D do not correspond to any standard laboratory reagent of this kind. The chemistry is worth one line: nitric acid oxidises the gold and the chloride from hydrochloric acid holds the resulting ions in solution, so each acid does what the other cannot. Aqua regia is used to test the purity of gold and to recover precious metals.

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 A, complete combustion of fuel. When enough air reaches the burner, every carbon atom of the fuel is oxidised fully to carbon dioxide and the flame is blue and hot, giving the maximum heat for the gas consumed. Option B is wrong because ordinary air contains nitrogen and oxygen with only traces of hydrogen, and the colour of the flame has nothing to do with hydrogen in the atmosphere. Option C is wrong because hazardous combustion is not a chemical term at all and describes nothing; the danger in a burner lies in incomplete burning, which releases poisonous carbon monoxide. Option D is wrong because insufficient oxygen produces the opposite result, a yellow sooty flame in which unburnt carbon particles glow, and the remedy is to clean the air holes of the burner so that more air is drawn in.

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 C, silver. Silver has the highest electrical conductivity of all metals and also the highest thermal conductivity, but it is costly and tarnishes, so it is used only in specialised contacts and instruments. Option A, copper, comes next and is the metal actually used for household and industrial wiring, because it combines high conductivity with reasonable cost and good ductility; students who answer from everyday use rather than from the property pick this one. Option B, aluminium, is a lighter and cheaper conductor used for overhead transmission lines, where weight matters more than conductivity per unit area. Option D, gold, conducts well and does not corrode, so it is used to plate delicate electronic contacts, but it ranks below silver and copper. Remember the order: silver, then copper, then gold, then aluminium.

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, catenation. Catenation is the self-linking of atoms of the same element, and carbon shows it more strongly than any other element because the carbon to carbon bond is short and exceptionally strong, which is why chains of many carbon atoms remain stable. Option A is wrong because tetravalency is the separate property of having four bonds available, which lets carbon hold four other atoms; the two properties together explain the huge number of carbon compounds. Option C is wrong because isomerism is the existence of different structures with the same molecular formula, such as the two forms of butane, and it is a consequence of catenation rather than its name. Option D is wrong because allotropy is the existence of an element in different physical forms, such as diamond, graphite and fullerene.

The correct answer is D, Black. In the colour code used for fire extinguishers, a black band or label marks a carbon dioxide extinguisher. The body of the cylinder is signal red and a coloured patch near the label tells you the filling at a glance, so the right cylinder can be picked in a hurry. A carbon dioxide extinguisher works by smothering: the gas is heavier than air, so it pushes oxygen away from the fuel, and it also chills the surface as it expands out of the horn. Because it does not conduct electricity and leaves no residue, it is the choice for live electrical equipment, switchboards, laboratories and computer rooms. Option A is wrong because a red band marks a plain water extinguisher, used on wood and paper fires. Option B is wrong because blue marks dry powder, the all-purpose filling for liquid and gas fires. Option C is wrong because cream, not white, is the colour for a foam extinguisher. Exam tip: red — water, cream — foam, blue — dry powder, black — carbon dioxide, yellow — wet chemical.

The correct answer is A, lead. Galena is lead sulphide, the principal ore from which lead is obtained; being a sulphide it is concentrated by froth flotation and then roasted in air to the oxide before reduction. Option B, mercury, is obtained from cinnabar, which is mercury sulphide, and the two sulphides are often placed together in matching questions. Option C, aluminium, comes from bauxite, a hydrated oxide, and because aluminium is highly reactive the oxide is reduced by electrolysis rather than by carbon. Option D, iron, comes from haematite and magnetite, both oxides, and magnetite is the one separated magnetically. A short list is worth memorising in ore-and-metal pairs: galena for lead, cinnabar for mercury, bauxite for aluminium, calamine and zinc blende for zinc, and copper pyrites for copper.

The correct answer is C, Red color scatters less than other colors. At sunset the Sun is close to the horizon, so its light travels through a much thicker layer of atmosphere before it reaches the eye. Air molecules scatter short wavelengths, blue and violet, far more strongly than long ones; this is Rayleigh scattering, in which the scattering falls off as the fourth power of the wavelength. Over that long slanting path almost all the blue is scattered sideways out of the beam, and mostly the long-wavelength red and orange light survives to reach us, so the Sun and the sky around it look red. Option A is wrong because sunlight is white and contains all seven colours. Option B is wrong because red is scattered the least, not the most; blue is scattered most, which is why the midday sky is blue. Option D is wrong because the effect lies in the atmosphere, not in the sensitivity of the eye. Exam tip: Rayleigh scattering gives a blue sky at noon and a red Sun at sunrise and sunset.

The correct answer is B. In graphite every carbon atom is bonded to only three others within a layer, so the fourth valence electron of each atom is free to move along the layer, and moving electrons constitute an electric current. Option A is wrong because pure graphite conducts by itself; impurities are not the reason, and the same conduction is seen in synthetic graphite of high purity. Option C is wrong because diamond and graphite are both made of carbon alone, which is the whole point of calling them allotropes; only the arrangement of atoms differs. Option D is wrong because diamond actually has an extremely high melting point owing to its rigid three-dimensional network, and melting point in any case does not decide conduction. In diamond each atom is bonded to four others, so no electron is left free.

The correct answer is B, zinc. In galvanisation iron or steel is given a coating of zinc, usually by dipping it in the molten metal, and the coating protects the iron in two ways: it keeps out air and moisture, and because zinc is more reactive than iron it corrodes in place of the iron even where the coating has been scratched. Option A, tin, is used to coat steel in the tinplate of food cans, a process called tinning, which protects only while the coating is intact. Option C, chromium, is applied by electroplating for shine and corrosion resistance and is also alloyed into stainless steel along with nickel. Option D, nickel, is likewise an electroplating and alloying metal. Recall that rusting needs both oxygen and moisture, so a coating, paint, oil or grease that keeps either away prevents it.

The correct answer is A, a CH2 unit and fourteen units of mass. Going from methane to ethane, or from ethanol to propanol, adds one carbon atom of mass twelve and two hydrogen atoms of mass one each, which is fourteen in all, and it is this fixed step that defines a homologous series. Option B is wrong because CH3 is a group, not the difference between successive members; a compound cannot differ from another by an odd fragment of this kind and remain a stable molecule of the same series. Option C is wrong because C2H4 would be a jump of two members at once, skipping one homologue. Option D is wrong because CH4 is the whole molecule of methane rather than the step of the series. Members of such a series share the same functional group and show a gradual change in boiling point and density.

The correct answer is B, aluminium oxide. An amphoteric oxide reacts with both acids and bases to form salts, and aluminium oxide does exactly that, behaving as a base towards hydrochloric acid and as an acid towards sodium hydroxide; zinc oxide is the other amphoteric oxide asked in examinations. Option A, sodium oxide, is a typical metal oxide and therefore basic, dissolving in water to give sodium hydroxide, a strong alkali. Option C, carbon dioxide, is a non-metal oxide and therefore acidic, dissolving in water to give carbonic acid, which is why it turns moist blue litmus red. Option D, sulphur dioxide, is likewise acidic and gives sulphurous acid in water. Remember the rule and its two exceptions: metal oxides are basic, non-metal oxides are acidic, and the oxides of aluminium and zinc are amphoteric.