Dear student
ketone and aldehyde are functional isomers: CH3-CH2-CHO and CH3-CO-CH3.
Alcohol and ether are functional isomers: CH3-CH2-CH2-OH and CH3-CH2-O-CH3
Caboxylic acid and esters are functional isomers: CH3-CH2-COOH and CH3-COO-CH3.
so your answer is only aldehyde and ketone are functional isomers, alcohol is not.
Regards