Nitrogen, a component of air is used for

Nitrogen gas (N₂) makes up about 78% of the atmosphere and has several important industrial uses. One of the most significant is the production of nitric acid (HNO₃).

The industrial production of HNO₃ occurs in two stages:

1. Haber process: Nitrogen reacts with hydrogen at high temperature and pressure in the presence of an iron catalyst to produce ammonia:
   \[\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)\]
2. Ostwald process: Ammonia is then oxidised over a platinum-rhodium catalyst to produce nitrogen monoxide, which is further oxidised and dissolved in water to form nitric acid:
   \[4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O}\]
   \[2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2\]
   \[3\text{NO}_2 + \text{H}_2\text{O} \rightarrow 2\text{HNO}_3 + \text{NO}\]

The other options are incorrect: margarine production uses hydrogen (not nitrogen) for hydrogenation of vegetable oils; nitrogen is not used in manufacturing oil; and while liquid nitrogen can serve as a coolant, the question refers to nitrogen as a component of air used in chemical production.