8 KMnO4 (aq) + 7 H2SO4 (aq) + 5 Na2S2O3 (aq) → 8 MnSO4 (aq) + 5 Na2SO4 (aq) + 4 K2SO4 (aq) + 7 H2O (l)
This is an oxidation-reduction (redox) reaction:
8 MnVII + 40 e- → 8 MnII (reduction)
10 SII - 40 e- → 10 SVI (oxidation)
KMnO4 is an oxidizing agent, Na2S2O3 is a reducing agent.