PbS + 4H₂O₂ →PbSO₄ + 4H₂O. In this reaction PbS undergoes

$\mathrm{Pb}\stackrel{-2}{\mathrm{S}}+4{\mathrm{H}}_2{\mathrm{O}}_2 \to \mathrm{Pb}\stackrel{+6}{\mathrm{S}}{\mathrm{O}}_4 + 4{\mathrm{H}}_2\mathrm{O}$

In PbS, sulphur has -2 oxidation state and it undergoes oxidation and change its oxidation state to +6.