Explanation

(b)
Stephen’s reduction Aldehyde can be prepared from alkyl cyanides. $e.g.,$
$CH_{3} - C \equiv N + 2\lbrack H\rbrack\underset{Ether}{\overset{\ \ \ SnCl_{2}/HCl\ \ \ }{\rightarrow}}CH_{3} - CH = NH.HCl$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow H_{2}O/H^{+}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ CH_{3}CHO + NH_{4}Cl$
acetaldehyde