A. Hydroxyl group (-OH)
B. Carbonyl group (-CHO)
C. Carboxyl group (-COOH)
D. Amino group (-NH2)
Answer: Carboxyl group (-COOH)
What is the distinguishing functional group in carboxylic acids?
Additional Information: Carboxylic acids contain the carboxyl group (-COOH), which is responsible for their acidic properties.