10 HNVO3 + 2 I20 5 N2IIIO3 + 4 HIVO3 + 3 H2O

This is an oxidation-reduction (redox) reaction:

4 I0 - 20 e- 4 IV (oxidation)

10 NV + 20 e- 10 NIII (reduction)

Change the oxidation states