Which of the following natural fibres is a protein?

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 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 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 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.

The correct answer is B, hexamethylenediamine and adipic acid. Nylon-6,6 is a polyamide formed when hexamethylenediamine condenses with adipic acid, with a molecule of water eliminated at each linkage; the name records that each monomer contributes a chain of six carbon atoms. It is used for ropes, tyre cord, brush bristles and parachute fabric. A is wrong because caprolactam alone gives nylon-6, a related but different polyamide. C is wrong because ethylene glycol with terephthalic acid gives the polyester terylene, also called dacron, and in bottle form polyethylene terephthalate. D is wrong because phenol with formaldehyde gives bakelite, a thermosetting plastic and not a fibre at all. The naming rule is worth carrying into the hall: a nylon with two numbers is made from two monomers, one supplying the diamine and the other the diacid, while a nylon with one number comes from a single monomer, so nylon-6,6 must be the pair and nylon-6 the single one.