General Science Mixed Quiz: Set 69

The correct answer is A, 1 and 3. A compound microscope uses two convex lenses, and its magnification depends on the tube length.

The objective is a convex lens of very short focal length that forms a real, enlarged image of the specimen. The eyepiece is also a convex lens and works like a magnifying glass on that image. The total magnification is roughly (L/fo) × (D/fe), where L is the tube length, D is 25 cm, the least distance of distinct vision, and fo and fe are the focal lengths of the objective and eyepiece. So a longer tube gives more magnification, while a longer focal length gives less.

B is wrong: statement 3 is true, but statement 1 is also true, so 3 alone is incomplete.

C is wrong: statement 4 is false, because the eyepiece is convex, not concave.

D is wrong: statement 2 is false, since magnification falls as the objective's focal length rises, and statement 4 is false as well.

Exam tip: microscope = two convex lenses, objective of short focal length; telescope objective has a long focal length.

The correct answer is B, Concrete. Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The cement and water react in a process called hydration, which sets into a hard mass and binds the aggregate together. A common ratio for ordinary work is one part cement, two parts sand and four parts gravel, written as 1:2:4. Concrete is strong in compression but weak in tension, so steel bars are embedded in it to make reinforced cement concrete, the material of most modern buildings, bridges and dams.

Option A, mortar, is cement or lime with sand and water only, with no coarse aggregate, and is used to join bricks. Option C, slurry, is any thin, pourable mix of a solid in a liquid. Option D, a moderator, is the material that slows neutrons in a nuclear reactor.

Exam tip: mortar has no gravel; concrete has gravel; adding steel gives RCC.

The correct answer is C, wool. Wool is the fleece of sheep and other animals and is made of the protein keratin, so it is a protein fibre; silk, which is the protein fibroin, is the other natural fibre of this kind, and both come from animals. A, cotton, is wrong because the cotton fibre is almost pure cellulose, a carbohydrate polymer obtained from the seed hair of the cotton plant. B, jute, is wrong because jute is a bast fibre from the stem of the jute plant and is also cellulose, with some lignin. D, flax, is wrong for the same reason, being the cellulose stem fibre from which linen is woven. The rule to carry into the examination hall is simple: fibres of animal origin are protein and fibres of plant origin are cellulose.

The correct answer is B, Stoichiometry. Stoichiometry is the branch of chemistry that measures how much of each reactant is used up and how much of each product is formed in a reaction, working from the balanced chemical equation. The coefficients of a balanced equation give the ratio in moles, and from that ratio a chemist can work out masses, volumes of gases and numbers of particles, identify the limiting reagent and calculate the percentage yield. The word comes from the Greek stoicheion, meaning element, and metron, meaning measure. Option A is wrong because mole fraction is the ratio of the moles of one component to the total moles in a mixture, a way of stating concentration. Option C is wrong because mass per cent gives the mass of a component present in 100 units of mass of the solution. Option D is wrong because molarity is the number of moles of solute dissolved in one litre of solution. Exam tip: stoichiometry works from the balanced equation, while mole fraction, molarity and mass per cent only express concentration.

The correct answer is C, R. H. Whittaker. Robert Harding Whittaker proposed the five kingdoms Monera, Protista, Fungi, Plantae and Animalia in 1969, using cell structure, body organisation, mode of nutrition, reproduction and evolutionary relationships as the criteria of division. A is wrong because Ernst Haeckel proposed a three-kingdom system by adding Protista to Plantae and Animalia. B is wrong because Carl Woese came later and, working from the chemistry of ribosomal nucleic acid, proposed the three domains Archaea, Bacteria and Eukarya, splitting the old Monera. D is wrong because Herbert Copeland proposed a four-kingdom system in which the bacteria were separated from the Protista, a step between Haeckel and Whittaker. Remember the sequence of systems as two kingdoms by Linnaeus, three by Haeckel, four by Copeland, five by Whittaker and three domains by Woese, because questions are often set on who came after whom.

The correct answer is D, stomata. The tiny pores on the surface of a leaf, found mostly on its lower side, are called stomata.

Each stoma is a slit guarded by two bean shaped guard cells, which swell to open it and shrink to close it. Through these pores the plant takes in carbon dioxide for photosynthesis and gives out oxygen, and water vapour escapes through them in the process called transpiration. Having them on the shaded lower surface reduces the loss of water. Floating plants such as the water lily carry their stomata on the upper surface instead, and fully submerged plants have almost none.

A is wrong: pore is only the general word for an opening and is not the botanical term. B is wrong: opening is likewise a plain description, not a name. C is wrong: cilia are tiny hair like structures that help some cells and organisms move, and they are not found on leaves.

Exam tip: stomata are leaf pores guarded by guard cells, mostly on the lower surface, used for gas exchange and for transpiration.

The correct answer is C, Infrared and microwave radiations. Both kinds of radiation carry energy that food absorbs as heat, and both are used in everyday kitchens.

Infrared radiation is the heat radiation given out by hot bodies: a grill, a toaster, an oven element or glowing coals cook the surface of food mainly by infrared rays. A microwave oven uses microwaves of about 2.45 GHz; water molecules in the food are polar, so they keep turning with the oscillating field and the friction heats the food from within. So two different bands of the spectrum are put to use in cooking.

A is wrong: infrared is used, but it leaves out the microwave oven.

B is wrong: microwaves are used, but grills and toasters cook with infrared.

D is wrong: X-rays, gamma rays and ultraviolet are harmful ionising or high-energy radiations and radio waves carry too little energy; none of them is used to cook.

Exam tip: microwave oven = about 2.45 GHz, heats water molecules; grill and toaster = infrared.

The correct answer is A, 1 and 4. Hooke's law holds only as far as the limit of proportionality, and that limit is either equal to or lower than the elastic limit, so statements 1 and 4 are the correct pair. Hooke's law says stress is proportional to strain, which is the straight part of the stress-strain graph; the point where the curve leaves the straight line is the limit of proportionality. A little beyond it the material still springs back to its original shape, and the last point at which it does so is the elastic limit. For most metals the two points lie very close together and for an ideal material they coincide. B is wrong because statement 2 extends the law past the straight part of the graph, where stress and strain are no longer proportional. C and D are wrong because statement 3 says always less, while the two limits may also be equal. Exam tip: order the four points as proportionality limit, elastic limit, yield point, ultimate stress.

The correct answer is B, cryolite. Pure alumina melts at a very high temperature, so it is dissolved in molten cryolite, which is sodium aluminium fluoride, usually with a little fluorspar added; this brings the working temperature down sharply and makes the melt a good conductor. Aluminium collects at the carbon-lined cathode at the bottom of the cell and oxygen is set free at the carbon anodes, which slowly burn away and must be replaced. A is wrong because bauxite is the ore from which alumina is first purified by the Bayer process; the ore itself is not electrolysed. C is wrong because molten sodium chloride is electrolysed in Down's process to obtain sodium metal and chlorine. D is wrong because limestone is a flux of the blast furnace in iron making and has no role in this cell.

The correct answer is C, fish farming. Pisciculture is the rearing of fish in ponds, tanks and other managed waters, the Latin word piscis meaning fish. It is a branch of aquaculture and India is one of the largest fish producers in the world; the Blue Revolution is the name given to the planned growth of fish output, and rohu, catla and mrigal are the common Indian carps raised in ponds. A is wrong because the rearing of honey bees is apiculture, which gives honey and beeswax. B is wrong because the rearing of silkworms is sericulture, in which the mulberry-fed Bombyx mori gives most of the world's silk. D is wrong because the rearing of birds is aviculture, and the keeping of fowl for eggs and meat is poultry farming. Exam tip: learn the culture words together - pisciculture fish, apiculture bees, sericulture silkworms, aviculture birds, horticulture fruits and vegetables, floriculture flowers.

The correct answer is C, Thiourea (accelerator). Accelerators speed up the vulcanisation of rubber; they are not a part of paint.

An oil paint is made of a pigment that gives colour and covering power, a vehicle or drying oil such as linseed oil that binds the film, a thinner that makes it easy to spread, a drier that speeds up hardening, fillers or extenders that add body, and an anti-skinning agent that stops a skin forming in the tin. Titanium dioxide is the most widely used white pigment, turpentine is the classic thinner, and polyhydroxy phenols are used as anti-skinning agents. Thiourea and similar compounds belong to rubber technology, where accelerators shorten the time sulphur takes to cross-link rubber.

A is wrong: turpentine oil is a standard thinner in paint.

B is wrong: polyhydroxy phenols are used in paint as anti-skinning agents.

D is wrong: titanium dioxide is the main white pigment in paints.

Exam tip: paint = pigment + vehicle (linseed oil) + thinner (turpentine) + drier + filler + anti-skinning agent.

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, Bombyx mori, the mulberry silkworm, the only fully domesticated insect of the silk group and the source of most of the world's raw silk. Option A, Antheraea mylitta, is the tropical tasar silkworm, which lives in the open on Asan and Arjun trees. Option C, Samia ricini, is the eri silkworm, reared on castor leaves, whose broken fibre is spun rather than reeled. Option D, Kerria lacca, is not a silkworm at all but the lac insect, a scale insect whose female secretes the resin called lac. The way to keep the four apart is to attach each to its host plant: mulberry for Bombyx mori, Asan and Arjun for tasar, castor for eri and Som for muga. Note also that this insect has been bred by people for so long that the adult moth can barely fly and depends entirely on rearers, which is what makes it the one truly domesticated silk insect.

The correct answer is B, A bottle opener. Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort. In a bottle opener the rim of the cap is the fulcrum at the tip, the cap being lifted is the load in the middle, and your hand applies the effort at the far end. Such levers always multiply force because the effort arm is longer; a wheelbarrow and a nutcracker work the same way. A, A pair of scissors, is a first class lever, with the pivot between the effort and the load. C, A cricket bat, is a third class lever: the lower hand applies the effort between the top hand, which acts as the fulcrum, and the ball. D, A bow and arrow, works by storing energy in the bent bow like a spring, not by placing the load between the fulcrum and the effort. Exam tip: first class has the fulcrum in the middle, second class the load in the middle, third class the effort in the middle.

The correct answer is B. A short-sighted (myopic) person sees near things clearly but distant things blurred, and a concave lens corrects it.

In myopia the eyeball is too long or the eye lens too strongly curved, so light from a distant object comes to a focus in front of the retina instead of on it. The far point of the eye moves closer than infinity. A concave (diverging) lens of suitable power spreads the incoming rays slightly, so they focus exactly on the retina. Its power is negative, measured in dioptres.

A is wrong: blurred near vision with clear distant vision is long-sightedness (hypermetropia), and both the defect and the lens are mismatched here.

C is wrong: it describes hypermetropia but pairs it with a concave lens.

D is wrong: the symptoms are right for myopia, but a convex lens would make it worse.

Exam tip: myopia = near clear, far blurred, concave lens; hypermetropia = far clear, near blurred, convex lens; presbyopia = age, often bifocals.

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 C, Chlamydomonas. Chlamydomonas is a unicellular, flagellated member of the Chlorophyceae, the green algae, in which chlorophyll a and b give the plant its grass-green colour and the food is stored as starch. A is wrong because Laminaria is a kelp and belongs to the Phaeophyceae or brown algae, in which the pigment fucoxanthin masks the chlorophyll and the stored food is laminarin and mannitol. B is wrong because Sargassum is also a brown alga, the floating weed that gives the Sargasso Sea its name. D is wrong because Fucus, the rockweed of cold shores, is again a brown alga. Of the four, only Chlamydomonas carries the green pigments without a masking one, so only it is a green alga. A quick rule for the paper is that a name ending in the Chlorophyceae group is green, while kelps and rockweeds of cold seas are brown and are stored as laminarin rather than starch.

The correct answer is C, zinc. Galvanisation is the coating of iron or steel with zinc, usually by dipping the article in molten zinc, and it protects the iron twice over: the layer keeps out air and moisture, and because zinc is the more reactive metal it corrodes in place of the iron even where the coating is scratched, which is sacrificial protection. A is wrong because the coating of tin on iron, as on the sheet of food cans, is called tinning; it protects only so long as it is unbroken, since tin is less reactive than iron. B is wrong because chromium plating, done by electrolysis, is used on taps and car fittings mainly for a bright and hard surface. D is wrong because nickel plating is likewise an electroplating process used on machine parts and cheap jewellery, often as an undercoat below chromium.

The correct answer is C, Assam. Muga silk comes from Antheraea assamensis, reared on Som and Soalu trees of the Brahmaputra valley, and Assam's muga carries a Geographical Indication tag. Option A is wrong as an answer to this question although Karnataka leads the country in mulberry silk, which is a different variety; students who remember only the words largest silk producer mark it wrongly. Option B is wrong because West Bengal is known for mulberry silk and for the research institute at Berhampore, not for muga. Option D is wrong because Jharkhand is famous for tasar silk and, above all, for lac. Remember the pairing: mulberry with Karnataka, muga with Assam, tasar with Jharkhand and Chhattisgarh. One more fact from this topic is often paired with the state: muga is reeled into a golden yarn that needs no dyeing, and its natural colour is the reason it is prized.

The correct answer is C, species. A species is a group of organisms that resemble one another in all essential characters and that can interbreed to produce fertile offspring; it is the smallest and the basic unit of classification, and all higher ranks are built by grouping species together. A is wrong because a genus is a group of closely related species, as Panthera holds the lion, the tiger and the leopard, so it stands one rank above the basic unit. B is wrong because a family is a group of related genera and is therefore wider still. D is wrong because an order is a group of related families, standing two ranks above family and far from being the basic unit of classification. A simple test in the examination hall is that the basic unit must be the group that cannot be divided further into smaller named groups of interbreeding organisms, and that description fits only the species.