5 K4(Fe(CN)6) + KMnO4 + 4 H2SO4 → 5 K3(Fe(CN)6) + MnSO4 + 3 K2SO4 + 4 H2O
This is an oxidation-reduction (redox) reaction:
MnVII + 5 e- → MnII (reduction)
5 FeII - 5 e- → 5 FeIII (oxidation)
KMnO4 is an oxidizing agent, K4(Fe(CN)6) is a reducing agent.