What group is written as -COOH?

• A. Hydroxyl Group
• B. Amino Acid
• C. Ester
• D. Carboxyl Group

Answer: (D)

The group written as -COOH is the carboxyl group. It features a carbonyl carbon (C=O) with a hydroxyl group (–OH) attached to the same carbon. This arrangement is the defining feature of carboxylic acids and explains its acidic behavior—the hydrogen on the –OH can be donated to solution, forming a carboxylate ion (-COO−). This group appears in compounds like fatty acids and amino acids. It’s different from a simple hydroxyl group (–OH) that lacks the carbonyl, and from esters, which have a carbonyl attached to an alkoxy group (–COO–) rather than –OH. An amino acid is a molecule that contains a carboxyl group, among other parts, rather than naming the group itself.