2 NaNIIIO2 + 2 NaI-I + 2 H2SO4 2 Na2SO4 + I20 + 2 NIIO + 2 H2O

This is an oxidation-reduction (redox) reaction:

2 I-I - 2 e- 2 I0 (oxidation)

2 NIII + 2 e- 2 NII (reduction)

Change the oxidation states