4 KNVO3 + Cr2IIIO3 + 2 KOH 2 KCrVIIO4 + 4 KNIIIO2 + H2O

This is an oxidation-reduction (redox) reaction:

4 NV + 8 e- 4 NIII (reduction)

2 CrIII - 8 e- 2 CrVII (oxidation)

Change the oxidation states