PbS (s) + 2 H2O2 (aq) → PbSO4 (s) + 2 H2 (g)
This is an oxidation-reduction (redox) reaction:
S-II - 8 e- → SVI (oxidation)
4 HI + 4 e- → 4 H0 (reduction)
4 O-I + 4 e- → 4 O-II (reduction)
PbS is a reducing agent, H2O2 is an oxidizing agent, H2O2 is an oxidizing agent.