6 NaI-I + 2 NaNVO3 + 4 H2SO4 4 Na2SO4 + 3 I20 + 2 NIIO + 4 H2O

This is an oxidation-reduction (redox) reaction:

6 I-I - 6 e- 6 I0 (oxidation)

2 NV + 6 e- 2 NII (reduction)

Change the oxidation states