When an organic compound was treated with sodium nitrite and hydrochloric acid in the ice-cold, nitrogen gas evolved copiously. The compound is :
A. A nitro compound
B. A primary amine
C. An aliphatic primary amine
D. An aromatic primary amine

Hint: Amine is a basic compound. It acts as a base. The reactions of primary amines are known as carbylamine reactions. Amines are of many types like primary amine, secondary amine, tertiary amine, aliphatic amine and aromatic amines.

Complete Step by Step Solution:
The chemical formula of sodium nitrile is $NaNO_2$.
When primary amine reacts with sodium nitrile and a strong acid such as hydrochloric acid or $HCl$ a primary alcohol, a salt such as sodium chloride and water is obtained along with nitrogen gas. This is a characteristic reaction of primary amine where nitrogen gas is evolved.
The above reaction of primary amine is as follows-
$RNH_2+NaNO_2+HCl\rightarrow ROH+NaCl+N_2+H_2O$
Thus in this reaction one mole of primary amine reacts with one mole of sodium nitrile and one mole of hydrochloric acid to form one mole of primary alcohol along with one mole of sodium chloride, one mole of water and one mole of nitrogen gas.
Thus the correct option is $B$.

Note: Primary amine is a compound which contains two hydrogen atoms attached to one nitrogen atom and one alkyl substituent attached with nitrogen atom. It is a basic compound and acts as a base as it can donate its lone pair of electrons to an acid.