Industrial preparation of nitric acid by Ostwald's process involves:

Ammonia is oxidise  to nitrogen oxides and on hydrolysis to give nitric acid.The preparation of nitric acid by Ostwald's process involves the following reactions:4NH3​(g)+5O2​ (g)⟶catalyst​4NO(g)+6H2​O(g)2NO(g)+O2​(g)⇋2NO2​(g)3NO2​+H2​O(g)→2HNO3​+NO(g)The first step involves the oxidation of NH3​ to NO.