4 Zn0 + Na3AsVO4 + 11 HCl 4 ZnIICl2 + As-IIIH3 + 3 NaCl + 4 H2O

This is an oxidation-reduction (redox) reaction:

AsV + 8 e- As-III (reduction)

4 Zn0 - 8 e- 4 ZnII (oxidation)

Change the oxidation states