Q.Which of the following compound is optically active ?

A carboxylic acid carries -COOH, structurally the fusion of a carbonyl and a hydroxyl on the same carbon, though with its own distinctive reactivity rather than the sum of the two parts. Aliphatic (R-COOH) or aromatic (Ar-COOH) depending on the attached group; higher aliphatic acids (roughly C12-C18, 'fatty acids') occur naturally as glycerol esters in fats. IUPAC naming mirrors aldehydes: longest chain through the -COOH carbon (always C1), '-e' replaced by '-oic acid' ('-dioic acid' for a diacid with -COOH at both ends, e.g. oxalic acid = ethane-1,2-dioic acid). STRUCTURALLY, the carboxyl carbon and both oxygens are sp2; three parallel, unhybridised p-orbitals (on carbon and both oxygens) overlap into a delocalised pi system, making RCOOH a genuine resonance hybrid rather than one fixed Lewis structure. Beca …