KNVO3 + Cr2IIIO3 + 4 KOHI 2 H20 + KNIIIO2 + 2 K2CrVIO4

This is an oxidation-reduction (redox) reaction:

4 HI + 4 e- 4 H0 (reduction)

NV + 2 e- NIII (reduction)

2 CrIII - 6 e- 2 CrVI (oxidation)

Change the oxidation states