Cr2VIO72- + 6 H+ + 2 SIVO2 S2VIIO82- + 2 (CrIII)3+ + 3 H2O

This is an oxidation-reduction (redox) reaction:

2 SIV - 6 e- 2 SVII (oxidation)

2 CrVI + 6 e- 2 CrIII (reduction)

SO2 is a reducing agent, Cr2O72- is an oxidizing agent.