The correct answer is D. Carboxylic acid.
A carboxylic acid is an organic compound that has the functional group -COOH. The carboxylic acid functional group is a carbon atom double bonded to an oxygen atom and also bonded to a hydroxyl group. The carbon atom is also bonded to a alkyl, alkenyl, aryl or other group, which is denoted by R in the question.
Ketones are organic compounds that have the functional group -C=O. The ketone functional group is a carbon atom double bonded to an oxygen atom. The carbon atom is also bonded to two alkyl groups.
Esters are organic compounds that have the functional group -COOR’. The ester functional group is a carbon atom double bonded to an oxygen atom and also bonded to an alkyl group (R) and an oxygen atom bonded to another alkyl group (R’).
Aldehydes are organic compounds that have the functional group -CHO. The aldehyde functional group is a carbon atom double bonded to an oxygen atom and also bonded to a hydrogen atom.
Therefore, the only option that has the functional group -COOH is D. Carboxylic acid.