Question

The acid which does not form an anhydride when treated with $P_2{O}_5$ is:

• A. Formic acid
• B. Acetic acid
• C. Propionic acid
• D. Benzoic acid

Answer 1

The correct option is A Formic acid

Phosphorus pentoxide is a dehydrating agent.
It abstracts a molecule of water from formic acid to form carbon dioxide.
$HCOOH\stackrel{P_2{O}_5}{\to }C{O}_2+H_{2}O$.
Thus, formic acid which does not form an anhydride when treated with $P_2{O}_5$.