2 CrIIII3-I + 21 Cl20 + 26 H2O 2 H2CrVIO4 + 6 HIVO3 + 42 HCl-I

This is an oxidation-reduction (redox) reaction:

6 I-I - 36 e- 6 IV (oxidation)

42 Cl0 + 42 e- 42 Cl-I (reduction)

2 CrIII - 6 e- 2 CrVI (oxidation)

Change the oxidation states