Cr2O3 (s) + 3 NaNO3 (aq) + 2 Na2CO3 (aq) → 2 Na2CrO4 (aq) + 3 NaNO2 (aq) + 2 CO2 (g)
This is an oxidation-reduction (redox) reaction:
3 NV + 6 e- → 3 NIII (reduction)
2 CrIII - 6 e- → 2 CrVI (oxidation)
NaNO3 is an oxidizing agent, Cr2O3 is a reducing agent.