2 As2IIIS3-II + 7 HClVIIO4 + 12 H2O 4 H3AsVO4 + 6 H2SVIO4 + 7 HCl-I

This is an oxidation-reduction (redox) reaction:

4 AsIII - 8 e- 4 AsV (oxidation)

6 S-II - 48 e- 6 SVI (oxidation)

7 ClVII + 56 e- 7 Cl-I (reduction)

Change the oxidation states