12 H2SO4 (aq) + 8 KMnO4 (aq) + 5 NiS (s) → 12 H2O (l) + 4 K2SO4 (aq) + 8 MnSO4 (aq) + 5 NiSO4 (aq)
This is an oxidation-reduction (redox) reaction:
8 MnVII + 40 e- → 8 MnII (reduction)
5 S-II - 40 e- → 5 SVI (oxidation)
KMnO4 is an oxidizing agent, NiS is a reducing agent.