Which functional group contains a carbonyl and a hydroxyl group?

The functional group that contains both a carbonyl group and a hydroxyl group is known as a carboxylic acid. A carboxylic acid features a carbonyl group (C=O) bonded to a hydroxyl group (–OH) on the same carbon atom. This structure is represented as –COOH.

In carboxylic acids, the presence of these two functional groups results in unique properties, such as acidity, because the hydrogen of the hydroxyl group can easily dissociate, allowing the molecule to donate a proton (H⁺) in solution. This is a defining characteristic of carboxylic acids and distinguishes them from other functional groups.

While aldehydes and ketones contain carbonyl groups, they lack the hydroxyl group. Aldehydes have a carbonyl group attached to at least one hydrogen atom, whereas ketones comprise a carbonyl group bonded to two other carbon atoms. Alcohols contain a hydroxyl group, but they do not contain a carbonyl group. Thus, the correct identification of the functional group that includes both the carbonyl and hydroxyl moieties is indeed carboxylic acid.