HAsIIIO2 + 3 Zn0 + 6 HCl 3 ZnIICl2 + As-IIIH3 + 2 H2O

This is an oxidation-reduction (redox) reaction:

AsIII + 6 e- As-III (reduction)

3 Zn0 - 6 e- 3 ZnII (oxidation)

HAsO2 is an oxidizing agent, Zn is a reducing agent.