2 N-IIIH3I + O20 3 H20 + 2 NIIO-II

This is an oxidation-reduction (redox) reaction:

6 HI + 6 e- 6 H0 (reduction)

2 N-III - 10 e- 2 NII (oxidation)

2 O0 + 4 e- 2 O-II (reduction)

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