General Science Mixed Quiz: Set 39

The correct answer is A, ionic compound. Sodium is a metal that gives up an electron easily and chlorine is a non-metal that accepts one, so the two form sodium chloride, an ionic compound. A sodium atom has one electron in its outermost shell and loses it to become a sodium ion with a positive charge; a chlorine atom is short of one electron and gains it to become a chloride ion with a negative charge. The opposite charges attract strongly, and this electrostatic attraction is the ionic bond in common salt, NaCl. B is wrong because a covalent compound is formed when two non-metals share electrons, as in water or methane. C is wrong because a coordinate bond needs a lone pair donated to an electron-deficient atom, which is not the case here. D is wrong because a metallic bond forms between metal atoms only, and chlorine is not a metal. Exam tip: metal plus non-metal gives an ionic compound.

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 C, litmus solution is a purple dye which is extracted from lichen. Litmus is a natural indicator obtained from lichens, which are a partnership between an alga and a fungus, and in a neutral solution it shows a purple colour. The indicator turns red in an acid and blue in a base, so the pair red-in-acid and blue-in-base is the first test a student of chemistry learns. Litmus is also supplied as red and blue paper strips, and other natural indicators such as turmeric, red cabbage juice and the China rose petal work in the same way. A is wrong because the colour is right but the source is lichen, not moss. B is wrong on both counts, since the dye is purple and not orange and it comes from lichen. D is wrong for the same two reasons, naming an orange dye taken from moss. Exam tip: litmus is a purple dye from lichen - red in acid, blue in base.

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, buckminsterfullerene. It is a molecule of sixty carbon atoms arranged in a closed cage of pentagons and hexagons, exactly like the panels of a football, and it is named after the architect who designed domes of the same geometry. Option A is wrong because graphite is built of flat hexagonal layers stacked over one another, which makes it soft and slippery rather than cage-like. Option C is wrong because coke is the impure carbon left when coal is heated in the absence of air and is used in extracting metals; it is not a crystalline allotrope with a definite molecular formula. Option D is wrong because charcoal is likewise an amorphous form of carbon obtained from wood, valued for adsorbing gases and colouring matter rather than for any regular structure.

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 B, rayon. Rayon is made by dissolving the cellulose of wood pulp in a chemical and forcing the solution through fine holes to form filaments. Because it is made from a natural polymer rather than built from small molecules, it is called a regenerated or semi-synthetic fibre, and its silk-like sheen has earned it the name artificial silk.

Option A is wrong because nylon is fully synthetic, the first fibre made entirely from coal, water and air, with no plant material in it. Option C is wrong because silk is a natural animal fibre obtained from the cocoon of the silkworm and is not man-made at all. Option D is wrong because polyester, of which terylene is the best known form, is a fully synthetic fibre made from petroleum products. Only rayon starts from wood pulp.

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 B, lysosome. A lysosome is a membrane-bound sac of powerful digestive enzymes that breaks down worn-out organelles and any foreign particle the cell takes in; if the cell is damaged or starving, the sacs burst and the same enzymes digest the cell itself, which is why the name suicide bag is used. Option A is wrong because the ribosome is the site of protein synthesis and is called the protein factory of the cell. Option C is wrong because the centrosome, present in animal cells, organises the spindle fibres during cell division. Option D is wrong because the vacuole stores water, sap and waste and keeps a plant cell turgid, which is a storage function and not a destructive one. Two more nicknames belong with this set and are asked just as often: the mitochondrion is the powerhouse of the cell and the Golgi apparatus is its packaging and dispatch unit.

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, 273 K. Ice melts at 0 degrees Celsius, and 0 degrees Celsius is 273 K on the Kelvin scale. To change Celsius into Kelvin, add 273 to the Celsius reading, so 0 + 273 gives 273 K; the melting point of ice is usually written as 273.15 K in exact work. The Kelvin scale starts at absolute zero, the lowest temperature possible, which is -273 degrees Celsius, so a Kelvin value is never negative. A is wrong because -273 C is absolute zero, not the melting point of ice. C is wrong because 273 C is a very high temperature, far above boiling water. D is wrong because a temperature in Kelvin cannot be negative at all. Exam tip: remember the pair - ice melts at 0 C or 273 K, and water boils at 100 C or 373 K.

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 B, Colloidal solution is homogenous in nature. A colloid only looks uniform to the eye; it is in fact a heterogeneous mixture, so this is the statement that is not true. In a colloid the particles measure between one and one thousand nanometres, large enough to scatter light but too small to be seen or to settle. The two parts of a colloid are called the dispersed phase and the dispersing medium, as in milk, where droplets of fat are spread through water. A true solution such as salt in water is homogeneous and a suspension is plainly heterogeneous, while a colloid lies between the two and is counted as heterogeneous. A is true because the particles do stay spread evenly through the medium. C is true because the scattering of a beam of light by colloidal particles is the Tyndall effect. D is true because the particles are too light to settle under gravity. Exam tip: a true solution is homogeneous while a colloid and a suspension are heterogeneous.

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 C, butane and propane. The LPG supplied in household cylinders is mainly a mixture of butane and propane, two gases that turn liquid under moderate pressure. Both are saturated hydrocarbons got while refining crude oil or processing natural gas, and because they liquefy on compression, a cylinder holds far more fuel than the same volume of gas would. The gases have no smell of their own, so a strong-smelling compound called ethyl mercaptan is added to make a leak noticeable at once. LPG burns with a clean blue flame and leaves almost no residue, which makes it a far better home fuel than wood or coal. A is wrong because methane is the chief part of CNG and biogas, not of LPG. B is wrong because ethane is at most a minor component. D is wrong because hexane is a liquid at room temperature and serves as a solvent. Exam tip: LPG is butane plus propane, while CNG is mainly methane.

The correct answer is D, Ligament. A ligament is the connective tissue that joins one bone to another at a joint. It is very elastic and strong, and it holds the bones in place so that a joint can move without the bones slipping apart. Ligaments contain little matrix of their own and are stretched when a joint is twisted, which is what happens in a sprain. A is wrong because a tendon joins a muscle to a bone; tendons are fibrous and strong but have limited stretch, so the pull of a muscle is passed straight to the bone. B is wrong because cartilage is the smooth, flexible tissue that pads the ends of bones and shapes the nose and ear, cushioning the joint rather than tying the bones together. C is wrong because matrix is the material in which the cells of a connective tissue are embedded, not a structure by itself. Exam tip: ligament bone to bone, tendon muscle to bone.

The correct answer is A, Pigeon. Birds and mammals are warm-blooded, which means they keep their body temperature nearly constant whatever the temperature outside, and a pigeon is a bird. Such animals are called homeothermic or endothermic; they produce the heat they need by oxidising food, which is why they eat more for their body size. Reptiles, amphibians and fishes are cold-blooded, or poikilothermic, so their body temperature rises and falls with the surroundings. That is why many of them bask in the sun to warm up and become inactive in the cold season. B is wrong because a crocodile is a reptile and therefore cold-blooded. C is wrong because a toad is an amphibian and also cold-blooded. D is wrong because the body temperature of a fish follows the temperature of the water around it. Exam tip: only birds and mammals are warm-blooded, so every reptile, amphibian and fish in an option list is cold-blooded.

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, 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 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.