See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: An anhydride forms when two carboxylic acid groups that are in close enough proximity (typically on adjacent carbons) condense with loss of water to form a cyclic anhydride (five-membered ring). A dianhydride requires two such pairs of adjacent COOH groups, each pair forming one anhydride ring. Step 1 – Analyze structure (a): The four COOH groups are at positions 1, 2, 3, 4 of the benzene ring (all on one side). The pair at C1 and C2 are adjacent → can form one anhydride ring. The pair at C3 and C4 are adjacent → can form a second anhydride ring. Therefore, structure (a) — 1,2,3,4-benzenetetracarboxylic acid — can form a dianhydride with two five-membered anhydride rings. Step 2 – Analyze structure (b): The four COOH groups are at positions 1, 2, 4, 5 of the benzene ring. The pair at C1 and C2 are adjacent → can form one anhydride ring. The pair at C4 and C5 are adjacent → can form a second anhydride ring. Therefore, structure (b) — 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) — can also form a dianhydride (pyromellitic dianhydride, PMDA), which is a well-known industrial compound. Step 3 – Why not option (c): Both structures are capable of forming dianhydrides, so 'neither' is incorrect. Step 4 – Conclusion: Both (a) and (b) possess two pairs of adjacent COOH groups on the benzene ring, enabling each to form two cyclic anhydride rings, i.e., a dianhydride. Therefore, the correct answer is D.