2 H2O2 (aq) → O2 (g) + 2 H2O (l)
This is an oxidation-reduction (redox) reaction:
2 O-I - 2 e- → 2 O0 (oxidation)
2 O-I + 2 e- → 2 O-II (reduction)
H2O2 is both an oxidizing and a reducing agent (disproportionation (dismutation)).
This is a gas evolution reaction, O2 is the formed gas.