4 Zn0 + H3AsVO4 + 8 HCl 4 ZnIICl2 + As-IIIH3 + 4 H2O

This is an oxidation-reduction (redox) reaction:

AsV + 8 e- As-III (reduction)

4 Zn0 - 8 e- 4 ZnII (oxidation)

H3AsO4 is an oxidizing agent, Zn is a reducing agent.