The football-shaped allotrope of carbon containing sixty atoms is called

The correct answer is D, propane and butane. Liquefied petroleum gas is a mixture of these two saturated hydrocarbons, which are gases at ordinary pressure but turn liquid under moderate pressure, so a large quantity of fuel fits into a small cylinder; a strong-smelling compound is added so that a leak is noticed. Option A is wrong because ethene is an unsaturated gas used to make polythene and to ripen fruit, not as cooking fuel. Option B is wrong because ethyne, also called acetylene, is burnt with oxygen in welding torches for its very hot flame, and it is not supplied in domestic cylinders. Option C is wrong because propene is a raw material of the plastics industry, chiefly for polypropylene. Remember also that compressed natural gas, used in vehicles, is mainly methane, a different fuel from LPG.

The correct answer is D, five. Hexane, C6H14, can be drawn as a straight chain of six carbons, as two chains of five carbons with a methyl branch in different positions, and as two chains of four carbons carrying branches, which gives five different structures with the same molecular formula. Option A is wrong because three is the number of isomers of pentane, C5H12, and candidates who remember the smaller member often answer with it. Option B is wrong because six is not the count for any of the first few alkanes; the next member, heptane, has nine isomers. Option C is wrong because four corresponds to no alkane in this part of the series either. The sequence worth memorising is simple: butane two, pentane three, hexane five, heptane nine.

The correct answer is B, dienes. The prefix di stands for two and the ending ene for a carbon to carbon double bond, so a diene is a hydrocarbon carrying exactly two such bonds; buta-1,3-diene, the raw material of synthetic rubber, is the standard example. Option A is wrong because terpenes are a class of natural compounds built from isoprene units and found in the oils of plants; they may contain several double bonds but the name says nothing about the number. Option C is wrong because the ending yne refers to a triple bond, so a name of that kind would describe three triple bonds and not double bonds at all. Option D is wrong for the same reason: it would mean two triple bonds. Reading the prefix for the count and the ending for the kind of bond answers the whole family of such questions.

The correct answer is B, ethyne. An alkyne contains a carbon to carbon triple bond, which needs at least two carbon atoms, so the series begins with ethyne, C2H2, also called acetylene and used with oxygen in welding. Option A is wrong because propyne, with three carbon atoms, is the second member of the series, not the first. Option C is wrong because a compound called methyne cannot exist as an alkyne at all: methane has a single carbon atom and there is no second carbon for it to form a triple bond with, which is exactly the trap the option is meant to spring. Option D is wrong because butyne has four carbon atoms and is the third member. The general formula of the series is CnH2n-2, and putting n equal to two gives C2H2, confirming ethyne as the first member.

The correct answer is A, complete combustion of fuel. When enough air reaches the burner, every carbon atom of the fuel is oxidised fully to carbon dioxide and the flame is blue and hot, giving the maximum heat for the gas consumed. Option B is wrong because ordinary air contains nitrogen and oxygen with only traces of hydrogen, and the colour of the flame has nothing to do with hydrogen in the atmosphere. Option C is wrong because hazardous combustion is not a chemical term at all and describes nothing; the danger in a burner lies in incomplete burning, which releases poisonous carbon monoxide. Option D is wrong because insufficient oxygen produces the opposite result, a yellow sooty flame in which unburnt carbon particles glow, and the remedy is to clean the air holes of the burner so that more air is drawn in.