KNO3 (aq) + Cr2O3 (s) + 4 KOH (aq) → 2 H2 (g) + KNO2 (aq) + 2 K2CrO4 (aq)
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)
KOH is an oxidizing agent, KNO3 is an oxidizing agent, Cr2O3 is a reducing agent.