14 H3O+ + 6 (Br-I)- + Cr2VIO72- 2 (CrIII)3+ + 21 H2O + 3 Br20

This is an oxidation-reduction (redox) reaction:

6 Br-I - 6 e- 6 Br0 (oxidation)

2 CrVI + 6 e- 2 CrIII (reduction)

Change the oxidation states