General Science Mixed Quiz: Set 40

The correct answer is C, ionic bond. A metal loses electrons and a non-metal gains them, so the transfer makes oppositely charged ions that attract each other, and that attraction is an ionic bond. Metals have few electrons in the outermost shell and low ionisation energy, so they part with electrons to form cations; non-metals have high electron affinity and take up electrons to form anions. Magnesium oxide and calcium chloride are formed the same way as common salt. The resulting compounds are hard, have high melting points and conduct electricity when molten or dissolved. A is wrong because a hydrogen bond is a weak attraction between molecules, as in water, not a bond formed in such a reaction. B is wrong because a metallic bond is the attraction between metal ions and free electrons within a metal. D is wrong because a covalent bond forms when two non-metals share electrons. Exam tip: transfer of electrons gives an ionic bond, sharing gives a covalent bond.

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, statement d. Bacteria in the mouth break down leftover food particles and produce acid, not base, so statement d is the incorrect one. That acid lowers the pH inside the mouth, and once the pH falls below 5.5 the enamel, which is made of calcium phosphate and is the hardest material in the human body, begins to dissolve; this is how tooth decay starts, and it is also why a basic toothpaste is used to neutralise the acid. A is not the answer because methanoic acid, also called formic acid, really is present in the sting of nettle leaves and in ant stings, so statement a is correct. B is not the answer because acetic acid truly is the acid in vinegar, present at about five to eight per cent. C is not the answer because decay really does begin below pH 5.5. Exam tip: nettle and ants give formic acid, vinegar gives acetic acid and curd gives lactic acid.

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, Ethyl acetate. Ethyl acetate is an ester, and esters are the family of organic compounds known for a sweet, fruity smell. It is formed when ethanol reacts with acetic acid in the presence of a little concentrated sulphuric acid, a reaction called esterification, and its formula is CH3COOC2H5. Because of this pleasant smell, esters are used in perfumes, in artificial flavours and as the solvent in nail polish remover; the smell of ripe bananas and pineapples also comes from esters of this kind. A is wrong because ethyl alcohol, or ethanol, has a sharp spirit-like smell rather than a fruity one. B is wrong because acetic acid gives the pungent smell of vinegar. D is wrong because acetophenone is a ketone with a heavy, almost almond-like odour and not the light fruity note of an ester. Exam tip: ester means a fruity smell, and esterification means an alcohol with a carboxylic acid.

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 D, boric acid. Boric acid dissolves in water to give a true solution, in which the dispersed particles are individual molecules small enough to pass through a filter paper and even a parchment membrane, and the mixture shows no Tyndall effect. A true solution is therefore not a colloid.

Option A is wrong because milk is a colloid, an emulsion of liquid fat droplets dispersed in water. Option B is wrong because mud is a colloidal dispersion of fine soil particles in water, which is why it stays turbid for a long time before settling. Option C is wrong because butter is also a colloid, with water dispersed in fat, that is a gel-like emulsion. The rule to apply is that only a true solution is excluded from the colloidal state.

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, Schleiden and Schwann. Matthias Schleiden, a botanist, concluded that all plants are made of cells, and Theodor Schwann, a zoologist, reached the same conclusion for animals; together their statement became the cell theory. Option B is wrong because Robert Hooke only discovered and named the cell and Robert Brown discovered the nucleus, and neither framed a general theory. Option C is wrong because Charles Darwin is associated with natural selection and the origin of species while Gregor Mendel founded the science of heredity through his work on pea plants. Option D is wrong because James Watson and Francis Crick described the double helix structure of DNA in 1953, which belongs to molecular biology. One addition completes the theory and is often the second half of the question: Rudolf Virchow stated that every cell arises from a pre-existing cell, which ruled out the idea of cells forming on their own.

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, melting of ice. Melting of ice only changes the state of water from solid to liquid; no new substance is formed, so it is a physical change. In a physical change the shape, size or state may change but the chemical composition stays the same, and the change can usually be reversed - liquid water can be frozen back into ice. In a chemical change new substances with new properties are formed and the change is hard to reverse. B is wrong because milk setting into curd is a chemical change brought about by bacteria, which turn lactose into lactic acid. C is wrong because ripening of fruits involves chemical reactions that change starch into sugar. D is wrong because fermentation of grapes converts sugar into alcohol, a new substance. Exam tip: if no new substance appears and the change can be reversed, it is physical.

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 D, colloidal solution of two liquids. An emulsion is a colloid in which one liquid is spread as fine droplets through another liquid that does not mix with it. Milk is the common example, with droplets of fat spread through water, and butter is the reverse kind, with droplets of water held in fat. Soap and detergents work as emulsifying agents: they keep oil droplets suspended in water so that grease can be washed away. In an emulsion both the dispersed phase and the dispersing medium are liquids, and that is what the question is testing. A is wrong because it describes colloids in general and not an emulsion in particular. B is wrong because a true solution is homogeneous with particles of molecular size, while an emulsion is a colloid. C is wrong because distillation separates liquids by their boiling points and has nothing to do with colloids. Exam tip: an emulsion is liquid in liquid, while an aerosol is a liquid or solid in gas.

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 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, 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, 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, 2 gram of carbon. Three grams of hydrogen, 48 grams of oxygen and 42 grams of nitrogen each come to 1.5 moles, while two grams of carbon is only about 0.17 mole, so carbon holds a different number of particles. The number of moles is found by dividing the given mass by the molar mass, and equal moles always mean an equal number of particles. Hydrogen gas is H2 with a molar mass of 2, so 3 divided by 2 is 1.5 moles. Oxygen gas is O2 with a molar mass of 32, so 48 divided by 32 is 1.5 moles. Nitrogen gas is N2 with a molar mass of 28, so 42 divided by 28 is 1.5 moles. Carbon has an atomic mass of 12, so 2 divided by 12 is about 0.17 mole. A is wrong because 3 grams of hydrogen is 1.5 moles. B is wrong because 48 grams of oxygen is also 1.5 moles. C is wrong because 42 grams of nitrogen is 1.5 moles too. Exam tip: convert every mass to moles first.

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, 2 s. A simple pendulum about one metre long completes one full swing in roughly two seconds, and a pendulum of this length is called the seconds pendulum. The time period of a simple pendulum is T = 2 pi times the square root of L divided by g, where L is the length of the thread and g is the acceleration due to gravity, about 9.8 metres per second squared. Putting L = 1 metre gives T = 2 x 3.14 x the square root of 1 divided by 9.8, which comes to about 2.01 seconds. The period depends only on the length and on g, not on the mass of the bob or on how far it is pulled aside, so long as the swing is small. A is wrong because a 6 second period needs a thread about 9 metres long. B is wrong because a 4 second period needs a thread about 4 metres long. D is wrong because a 1 second period belongs to a thread of only about 25 centimetres. Exam tip: the period doubles only when the length becomes four times.