Explanation

(c)
The Hell-Volhard-Zelinsky reaction is used for preparing $\alpha$-halo acid.
$CH_{3} - CH_{2} - COOH\underset{- HCl}{\overset{{\ \ \ \ \ Cl}_{2}/P\ \ \ \ }{\rightarrow}}CH_{3} - CH - COOH$
$\ \ \ \ \ \ \ |$
$\ \ \ \ \ \ Cl$
$\propto$-chloropropanoic acid