(b)
$C_{2}H_{5}NH_{2}\overset{\ \ \ HNO_{2\ \ \ \ }}{\rightarrow}C_{2}H_{5}OH{\overset{\ \ \ {PCl}_{5}\ \ }{\rightarrow}C_{2}H_{5}Cl{\overset{\ \ \ \ \ NH_{3\ \ \ \ \ \ \ \ }}{\rightarrow}{\ C}_{2}H_{5}{NH}_{2}}}$
Ethyl amine ethyl alcohol ethyl chloride ethyl amine
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (A)\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (B)\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (C)$