Correct Option (b):
The characteristic pungent odour of garlic is primarily attributed to organosulphur compounds. Among these, allicin is the most significant. Allicin is not naturally present in intact garlic but is formed enzymatically from alliin (a sulphur-containing amino acid) when garlic cloves are crushed or chopped. This enzymatic conversion by the enzyme alliinase releases volatile sulphur compounds, which are responsible for the distinct aroma.
Incorrect Options:
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a chloro compound: Garlic's characteristic odour is not due to chloro compounds. These compounds are not the primary volatile aromatic constituents of garlic.
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a fluorine compound: Fluorine compounds are not naturally occurring in garlic in amounts that would contribute to its distinctive odour. The chemical composition responsible for garlic's aroma does not involve fluorine.
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acetic acid: Acetic acid is the primary component of vinegar and is known for its sharp, sour, vinegar-like smell. This odour is distinctly different from the characteristic pungent smell of garlic and is not responsible for it.