2 N-IIIH3 + 2 O20 N2IO-II + 3 H2O-II

This is an oxidation-reduction (redox) reaction:

2 N-III - 8 e- 2 NI (oxidation)

4 O0 + 8 e- 4 O-II (reduction)

NH3 is a reducing agent, O2 is an oxidizing agent.