3 KNVO3 + Cr2IIIO3 + 4 KOH 3 KNIIIO2 + 2 K2CrVIO4 + 2 H2O

This is an oxidation-reduction (redox) reaction:

3 NV + 6 e- 3 NIII (reduction)

2 CrIII - 6 e- 2 CrVI (oxidation)

KNO3 is an oxidizing agent, Cr2O3 is a reducing agent.