KNVO3 + Cr2IIIO3 + 4 KOH 2 K2CrIVO3 + KNIIIO2 + 2 H2O

This is an oxidation-reduction (redox) reaction:

NV + 2 e- NIII (reduction)

2 CrIII - 2 e- 2 CrIV (oxidation)

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