Question:
Which dicarboxylic acid in presence of a dehydrating agent is least reactive to give an anhydride :
Correct Option: 4,
Solution:
Adipic acid $\mathrm{CO}_{2} \mathrm{H}-\left(\mathrm{CH}_{2}\right)_{4}-\mathrm{CO}_{2} \mathrm{H} \underset{\text { dehydrating }}{\stackrel{\text { agent }}{\longrightarrow}}$
7 membered cyclic anhydride (Very unstable)