In neutral or Faintly alkaline medium, thiosulphate is oxidised almost quantitatively to sulphate ion according to reaction given below, 8MnO4−+3S2O32−+H2O→8MnO2+6SO42−+2OH− Here the Mn changes from Mn+7 to Mn+4 Thus overall change in its oxidation number would be of 3 .