8 N-IIIH3 + 3 Cl20 6 N-IIIH4Cl-I + N20

This is an oxidation-reduction (redox) reaction:

6 Cl0 + 6 e- 6 Cl-I (reduction)

2 N-III - 6 e- 2 N0 (oxidation)

Change the oxidation states