8 N-IIIH3 + 3 Br20 6 N-IIIH4Br-I + N20

This is an oxidation-reduction (redox) reaction:

6 Br0 + 6 e- 6 Br-I (reduction)

2 N-III - 6 e- 2 N0 (oxidation)

Br2 is an oxidizing agent, NH3 is a reducing agent.