Which of the following acids do not contain a carboxylic group?
A. Picric acid
B. Phthalic acid
C. Benzoic acid
D. Sulphurous acid
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A and D only
A carboxylic acid contains the carboxyl group, –COOH. Many compounds are called “acids” without having it: they may be phenols made acidic by other groups, or inorganic acids. So each name must be matched to its structure:
(A) Picric acid — Correct. It is 2,4,6-trinitrophenol, \( \ce{C6H2(NO2)3OH} \). It is strongly acidic because the three –\( \ce{NO2} \) groups stabilise the phenoxide ion, but its acidic group is a phenolic –OH.
(B) Phthalic acid — Incorrect. It is benzene-1,2-dicarboxylic acid, \( \ce{C6H4(COOH)2} \).
(C) Benzoic acid — Incorrect. It has a carboxyl group: \( \ce{C6H5COOH} \).
(D) Sulphurous acid — Correct. It is an inorganic acid, \( \ce{H2SO3} \), with no carbon at all.