As2IIIS3-II + 14 Cl20 + 20 H2O 2 H3AsVO4 + 3 H2SVIO4 + 28 HCl-I

This is an oxidation-reduction (redox) reaction:

2 AsIII - 4 e- 2 AsV (oxidation)

3 S-II - 24 e- 3 SVI (oxidation)

28 Cl0 + 28 e- 28 Cl-I (reduction)

As2S3 is a reducing agent, As2S3 is a reducing agent, Cl2 is an oxidizing agent.