This is an oxidation-reduction (redox) reaction:
2 HI + 2 e- → 2 H0 (reduction)
2 O-I - 2 e- → 2 O0 (oxidation)
H2O2 is an oxidizing agent, H2O2 is a reducing agent.
This is a gas evolution reaction, H2 and O2 is the formed gas.
Reactants:
Products: