General Science Mixed Quiz: Set 66

The correct answer is B. Limestone decomposes in the furnace to calcium oxide, a basic flux, which combines with the acidic silica gangue of the ore to form calcium silicate, a fusible slag that floats on the molten iron and is drawn off separately. Option A is wrong because the reduction of iron oxide is done by coke and by the carbon monoxide it generates, not by limestone; this is the classic carbon reduction used for moderately reactive metals. Option C is wrong because the heat comes from the burning of coke in the blast of hot air, and the decomposition of limestone actually absorbs heat. Option D is wrong because pig iron does take up carbon from the coke, giving it the highest carbon content of the iron products, but limestone has no part in that; wrought iron carries the least carbon and steel an intermediate amount.

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 B, carbon monoxide. When the oxygen supply is short, the carbon of the fuel is only partly oxidised and carbon monoxide is formed instead of carbon dioxide. Carbon monoxide is colourless and odourless, so it gives no warning, and it binds to the haemoglobin of blood far more strongly than oxygen does, forming carboxyhaemoglobin and starving the tissues of oxygen; this is what kills people who sleep in a closed room with a coal fire or a burning angithi. A is wrong because carbon dioxide is the product of complete combustion; it is a greenhouse gas and can suffocate in very large amounts, but it is not the poison meant here. C is wrong because sulphur dioxide comes from the sulphur in coal and petroleum and is a cause of acid rain. D is wrong because the oxides of nitrogen form at the high temperatures of engines and also cause acid rain and smog.

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 B, silk. Silk is the protein fibroin, spun by the silkworm, so it is a polymer made by a living organism and is therefore natural, like cellulose, starch, wool and natural rubber. A, bakelite, is wrong because it is a fully synthetic thermosetting plastic made in a factory by condensing phenol with formaldehyde, and it was in fact the first wholly synthetic plastic. C, Kevlar, is wrong because it is a synthetic aramid polymer, made from an aromatic diamine and an acid chloride, and used in bullet-resistant vests and helmets. D, Lexan, is wrong because it is the trade name of a synthetic polycarbonate used for unbreakable sheets, spectacle lenses and helmet visors. Remember the test: if the polymer is made by a plant or an animal it is natural, and if it is built in a reactor it is synthetic.

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.

The correct answer is D, 20 A. The working rule for charging a storage battery is that the charging current should be about one-tenth of the ampere-hour capacity of the battery, which is called the C by 10 rate. For a battery rated 200 ampere-hours, one-tenth of 200 gives 20 amperes, and at that rate a fully discharged battery takes roughly ten to twelve hours to charge. A rate much higher than this heats the plates, boils the electrolyte and shortens the life of the cell, while a much lower rate leaves the battery undercharged and allows sulphation. A, 12 A, and B, 15 A, are wrong because they are below the one-tenth value and are simply arbitrary figures for a 200 ampere-hour cell. C, 10 A, is the trap: it is one-twentieth of the rating, and candidates who remember the words ten per cent but apply them to the wrong number mark it.

The correct answer is B, Gamma rays. Gamma rays sit at the far end of the electromagnetic spectrum, with the shortest wavelength and therefore the highest frequency and energy. Arranged from the longest wave to the shortest, the spectrum runs radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All of them travel at the same speed in vacuum, so a shorter wave must have a higher frequency and each packet carries more energy. Gamma wavelengths are smaller than about 0.01 nanometre; they come out of the nucleus of a radioactive atom and are used to sterilise surgical instruments and to treat tumours. Option A is wrong because visible light measures roughly 400 to 700 nanometres, tens of thousands of times longer. Option C is wrong because infrared lies just beyond red and is longer than visible light, which is why we feel it as heat. Option D is wrong because X-rays are short but still longer than gamma rays, and they come from electrons, not the nucleus. Exam tip: the energy order is the reverse of the wavelength order.

The correct answer is B, nichrome. Nichrome is an alloy of nickel, chromium and iron with a high electrical resistance and a high melting point, and it does not oxidise easily when red hot, so a nichrome wire can glow for years without burning away; that combination makes it the standard material for the heating elements of irons, toasters, geysers and hair dryers. Option A is wrong because invar is an alloy of iron and nickel chosen for its very low thermal expansion and used in pendulums and measuring tapes, where heating must not change the length. Option C is wrong because duralumin, an alloy of aluminium with copper, magnesium and manganese, is a light structural alloy used in aircraft. Option D is wrong because solder, an alloy of lead and tin, has a low melting point by design and is used to join wires.

The correct answer is C, Bakelite. Bakelite is a thermosetting polymer, made by condensing phenol with formaldehyde, and once it has set under heat its chains are cross-linked, so it cannot be melted and moulded again. That hardness and poor conduction of heat and electricity are why bakelite is used for switches, plugs, handles of pans and radio cabinets; it was prepared by Leo Baekeland and was the first fully synthetic plastic. Melamine and urea-formaldehyde resins behave in the same way. A is wrong because polythene is a thermoplastic that softens on heating and can be recycled into new articles. B is wrong because PVC is also a thermoplastic, used for pipes, cable covers and raincoats. D is wrong because neoprene is a synthetic rubber, that is an elastomer, valued for resisting oil and petrol. Exam tip: thermosetting means bakelite, melamine and urea-formaldehyde; thermoplastic means polythene, PVC and polystyrene.

The correct answer is A, coal tar and coal gas. Destructive distillation means heating coal strongly in the absence of air, so that it decomposes instead of burning. The solid left behind is coke, which is almost pure carbon and is used as a reducing agent in the extraction of iron and other metals and as a smokeless fuel. The liquid that condenses is coal tar, a black mixture of about two hundred substances used to make dyes, drugs, explosives, plastics and naphthalene. The gas that escapes is coal gas, once piped for street lighting. B is wrong because petrol and diesel come from the fractional distillation of petroleum, not of coal. C is wrong because producer gas is made by passing air over hot coke and biogas by the anaerobic digestion of dung and waste. D is wrong because bitumen and paraffin wax are the heavy fractions of petroleum refining.

The correct answer is A, Bryophytes. Bryophytes live on land but still need water to complete reproduction, so they are called the amphibians of the plant kingdom. Mosses, liverworts and hornworts belong here. They grow in damp, shady places, have no true roots, stems or leaves and no vascular tissue, so water moves through them by simple absorption. Their male gametes swim to the egg through a film of water, which ties them to moist ground exactly as frogs are tied to ponds. Option B is wrong because thallophytes are the algae, mostly water plants that never left water. Option C is wrong because pteridophytes, the ferns, are the first plants with true vascular tissue, xylem and phloem. Option D is wrong because gymnosperms such as pine and cycas bear naked seeds and use pollen, not swimming gametes. Exam tip: bryophytes are amphibians of the plant kingdom, pteridophytes are the first vascular plants, and gymnosperms are the first seed plants.

The correct answer is B, ethene. Polythene, also written polyethene, is formed by the addition polymerisation of ethene, in which the double bond of each molecule opens and the units join into a long chain with nothing eliminated. A, ethyne, is wrong because ethyne, the old acetylene, carries a triple bond and is used in welding and in making other chemicals, not in making polythene. C, propene, is wrong because propene is the monomer of polypropylene, the plastic of ropes, bottle caps and furniture, and it is the commonest distractor here. D, vinyl chloride, is wrong because it is the monomer of polyvinyl chloride, the plastic of pipes, raincoats and cable covering. The same monomer, ethene, gives both low density and high density polythene; the difference lies in the pressure and the catalyst used.

The correct answer is C, Yeast, amoeba, bacteria. All three are unicellular, which means a single cell carries out every job of life. In a unicellular organism that one cell manages nutrition, respiration, movement and reproduction, while a multicellular body shares the work among tissues and organs. Yeast is a single-celled fungus used in baking and brewing, amoeba is a single-celled protozoan that moves and feeds with pseudopodia, and bacteria are single-celled organisms whose cells have no true nucleus. A is wrong because hydra, though a simple animal, is multicellular, with a body wall and tentacles made of many cells. B is wrong for the same reason, as sea anemone is a multicellular animal of the phylum Cnidaria, even though paramecium and bacteria are single-celled. D is wrong because only paramecium in that group is unicellular; hydra and sea anemone are both multicellular. Exam tip: unicellular – bacteria, amoeba, paramecium, yeast, chlamydomonas; multicellular – hydra, sea anemone, spirogyra.

The correct answer is C, 12 V. When cells are joined in parallel all their positive terminals are connected together and all their negative terminals together, so each cell is across the same two points and the voltage of the combination is the voltage of one cell, that is 12 volts. What the parallel arrangement does add is the current capacity: six identical cells in parallel can supply six times the current, or the same current for six times as long, and the internal resistance of the group falls to one-sixth of that of a single cell. B, 72 V, is wrong because adding the voltages is what happens in a series connection, where the positive of one cell is joined to the negative of the next. A, 6 V, and D, 2 V, are wrong because no method of grouping identical cells reduces the terminal voltage below that of one cell; 2 V happens to be the voltage of a single lead-acid cell, of which six in series make such a 12 volt battery.

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, it has a very low ignition temperature. A good fuel should have a moderate ignition temperature, not a very low one. A fuel that catches fire at a very low temperature is an inflammable substance and is dangerous to store, carry and handle, because a small spark or even a hot day can set it alight; petrol is useful but precisely for this reason it needs sealed containers and strict precautions. A is wrong as the answer because a high calorific value is certainly desirable: more heat is obtained from the same mass of fuel. B is wrong as the answer because a low ash content is desirable too, since ash is useless residue that has to be removed and that lowers the effective heat output. D is wrong as the answer because cheapness and ready availability are standard requirements of a good fuel, along with ease of storage and transport and the absence of harmful combustion products.

The correct answer is D, bakelite. Bakelite is made by condensing phenol with formaldehyde, and on moulding its chains join to one another by strong covalent cross-links into a single rigid network. Once set it cannot be softened by heating again, which is the definition of a thermosetting plastic and the reason bakelite is used for electrical switches, plug tops and the handles of pans. A, bioplastic, is wrong because the word describes any plastic made from a biological raw material or able to be broken down by organisms, and it names no single thermosetting material. B, bagasse, is wrong because bagasse is the fibrous residue left after sugarcane is crushed; it is used as fuel, for paper and for moulded tableware, but it is not a plastic. C, mycotecture, is wrong because it refers to building material grown from fungal mycelium, which again is not a thermosetting plastic.

The correct answer is B, the anode. The anode is the electrode joined to the positive terminal of the supply, so negatively charged ions, the anions, travel to it and give up electrons there; loss of electrons is oxidation. A is wrong because the cathode is joined to the negative terminal, attracts the positively charged cations and gives them electrons, so reduction, not oxidation, occurs there. The rule holds in a galvanic cell as well, where the anode is the negative terminal but is still the seat of oxidation, which is the point examiners test. C is wrong because the electrolyte is only the medium in which the ions move; the reactions happen where the ions meet the electrodes. D is wrong because a salt bridge belongs to a galvanic cell with two half-cells and merely completes the circuit while keeping the solutions electrically neutral; it is not a site of oxidation.

The correct answer is A, tetrafluoroethene. Teflon is polytetrafluoroethene, made by the addition polymerisation of tetrafluoroethene. The fluorine atoms shield the carbon chain so completely that the surface is chemically inert, water repellent and almost frictionless, and it holds its properties to high temperature, which is why it coats frying pans and is used for gaskets and seals. B, chloroprene, is wrong because it is the monomer of neoprene, a synthetic rubber used for oil seals and hoses. C, styrene, is wrong because it is the monomer of polystyrene, the material of disposable cups and, as expanded foam, of thermocol. D, caprolactam, is wrong because it is the monomer of nylon-6, used for fabric, fishing nets and machine parts. A useful memory link is that Teflon was found by accident in 1938, when a cylinder of tetrafluoroethene was found to hold a waxy white solid instead of the gas.