4 KI-I + 2 CuIISO4 2 CuII-I + I20 + 2 K2SO4

This is an oxidation-reduction (redox) reaction:

2 CuII + 2 e- 2 CuI (reduction)

2 I-I - 2 e- 2 I0 (oxidation)

Change the oxidation states