2 K3[Fe(CN)6] (aq) + 2 KOH (aq) + H2O2 (aq) → 2 K4[Fe(CN)6] (aq) + 2 H2O (l) + O2 (g)
This is an oxidation-reduction (redox) reaction:
2 FeIII + 2 e- → 2 FeII (reduction)
2 O-I - 2 e- → 2 O0 (oxidation)
K3[Fe(CN)6] is an oxidizing agent, H2O2 is a reducing agent.
This is a gas evolution reaction, O2 is the formed gas.