Cr2(SO4)3 + 6 KMnO4 + 16 KOH → 2 K2CrO4 + 3 K2SO4 + 6 K2MnO4 + 8 H2O
This is an oxidation-reduction (redox) reaction:
6 MnVII + 6 e- → 6 MnVI (reduction)
2 CrIII - 6 e- → 2 CrVI (oxidation)
KMnO4 is an oxidizing agent, Cr2(SO4)3 is a reducing agent.