Step 1: Understanding the Concept
Acetonitrile, \(\text{CH}_{3}\text{CN}\), is reduced by sodium in ethanol (Mendius reduction) to a primary amine.
Step 2: Find A
The product A is ethylamine, \(\text{CH}_{3}\text{CH}_{2}\text{NH}_{2}\).
Step 3: Find B
\(\text{NaNO}_{2}\) with dilute HCl produces nitrous acid. A primary aliphatic amine gives an unstable diazonium salt that loses \(\text{N}_{2}\) and forms the alcohol, so B is \(\text{CH}_{3}\text{CH}_{2}\text{OH}\).
Final Answer:
B is ethanol.
\[ \boxed{\text{(D) }\text{CH}_{3}\text{-CH}_{2}\text{-OH}} \]