Consider the following pairs of organic compounds: (I) o-Cresol and Benzyl alcohol (II) Propan-1-amine and N-methylethanamine (III) Butanoic acid and Methyl propanoate (IV) Pentan-2-one and Pentan-3-one (V) Propanal and Butanone The number of pairs that represent functional isomers is:

Step-by-step solution

Let us evaluate each pair to determine if they are functional isomers. Functional isomers must have the exact same molecular formula but different functional groups. (I) o-Cresol is a phenol ( -OH attached directly to the benzene ring), while Benzyl alcohol is an alcohol ( -OH attached to an sp^3 carbon). Both have the molecular formula C₇H₈O . They are functional isomers. (II) Propan-1-amine is a 1^ amine, and N-methylethanamine is a 2^ amine. Both have the molecular formula C₃H₉N . Amines of different degrees are