The commercial production of nitric acid involves the following chemical reactions: 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g)
2 NO (g) = O2 (g) → 2 NO2 (g)
3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO (g)
Which of these reactions are redox reactions?

In each redox reaction identify the element undergoing oxidation and the element undergoing reduction.