H2Cr2VIO7 + 6 H2S-II 2 Cr0 + 6 S0 + 7 H2O

This is an oxidation-reduction (redox) reaction:

6 S-II - 12 e- 6 S0 (oxidation)

2 CrVI + 12 e- 2 Cr0 (reduction)

Change the oxidation states