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