Enlist the main uses of nitrogen.

(N/A) $1$. In the manufacturing of $NH_3$ and industrial chemicals such as calcium cyanamide $(CaCN_2)$.
$2$. In the iron and steel industry to maintain an inert atmosphere.
$3$. As an inert diluent for reactive chemicals.
$4$. Liquid nitrogen is used as a refrigerant to preserve biological materials,food items,and in cryosurgery.