Which functional group is characteristic of carboxylic acids (-COOH)?

• A. Carboxylic acid
• B. Ester
• C. Ether
• D. Alcohol

Answer: (A)

The carboxyl group is the hallmark of carboxylic acids. It is written as -COOH, consisting of a carbonyl group (C=O) bonded to a hydroxyl group (–OH) on the same carbon. This arrangement creates a highly polar, resonance-stabilized unit and gives the hydrogen on the –OH a noticeable acidity. That combination—C=O plus O–H on the same carbon—is what defines the functional group of carboxylic acids.

Other options don’t fit because they lack this specific -COOH arrangement: an ester has a carbonyl attached to an alkoxy group (-COOR) but no hydroxyl on the same carbon; an ether is simply an R–O–R with no carbonyl; an alcohol has an -OH attached to carbon but no adjacent carbonyl.