5 KNO3 + Cr2(SO4) + 3 Na2CO3 → 5 KNO2 + 2 Na2CrO4 + Na2SO4 + 3 CO2
This is an oxidation-reduction (redox) reaction:
SII - 4 e- → SVI (oxidation)
5 NV + 10 e- → 5 NIII (reduction)
2 CrIII - 6 e- → 2 CrVI (oxidation)
Cr2(SO4) is a reducing agent, KNO3 is an oxidizing agent, Cr2(SO4) is a reducing agent.