2 KMnO4 (aq) + 5 KNO2 (aq) + 3 H2SO4 (aq) → 5 KNO3 (aq) + K2SO4 (aq) + 2 MnSO4 (aq) + 3 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 MnVII + 10 e- → 2 MnII (reduction)
5 NIII - 10 e- → 5 NV (oxidation)
KMnO4 is an oxidizing agent, KNO2 is a reducing agent.