2 KClVO3 + 3 FeIISO4 + 12 KOH 3 K2FeVIO4 + 2 KCl-I + 3 K2SO4 + 6 H2O

This is an oxidation-reduction (redox) reaction:

2 ClV + 12 e- 2 Cl-I (reduction)

3 FeII - 12 e- 3 FeVI (oxidation)

Change the oxidation states