What is the product of the following reaction?

$R-CH_2-NH_2$

The correct answer is Option (4) → $R-CH_2-NH_2$

Based on the image provided, the reduction of an alkyl nitrile ($R-CN$) using either catalytic hydrogenation ($H_2/Ni$) or chemical reduction with sodium amalgam in ethanol ($Na(Hg)/C_2H_5OH$) yields a primary amine ($R-CH_2NH_2$).

Reaction Mechanism

The process involves the addition of four hydrogen atoms across the triple bond of the nitrile group:

1. Hydrogenation/Reduction: The carbon-nitrogen triple bond ($C \equiv N$) is fully reduced to a single bond ($C-N$).
2. Product Formation: Two hydrogen atoms are added to the carbon atom and two are added to the nitrogen atom.
3. Result: This transforms the nitrile into a primary amine with the same number of carbon atoms.