KMnO4 acts as an oxidising agent. In neutral or faintly alkaline medium alkaline KMnO4 is reduced to MnO2.
8MnO4−+3S2O32−+H2O→8MnO2+6SO42−+2OH−
The change in oxidation state of manganese in this reaction is from +7 to +4. So, In this reaction overall change in oxidation state of manganese will be 3.