H2O2-I + 2 FeIISO4-II + 4 KO-IIH 2 FeIII(O-IIH)3 + 2 K2SO4-II

This is an oxidation-reduction (redox) reaction:

2 O-I + 2 e- 2 O-II (reduction)

2 FeII - 2 e- 2 FeIII (oxidation)

H2O2 is an oxidizing agent, FeSO4 is a reducing agent.