The colour of old lead paintings can be restored by washing them with a dilute solution of ${\mathrm{H}}_2{\mathrm{O}}_2$. The reaction is given below i.e.

$\underset{\mathrm{Litharge}}{\mathrm{PbO}}\stackrel{{\mathrm{H}}_2\mathrm{S}}{\to }\underset{\mathrm{Black}}{\mathrm{PbS}}\stackrel{{\mathrm{H}}_2{\mathrm{O}}_2}{\to }\underset{\mathrm{White}}{{\mathrm{PbSO}}_4}$

Here, hydrogen peroxide acts as oxidising agent because oxidation state of sulphur changes from $-2$ to $+6$ so $\mathrm{PbS}$ is oxidised to ${\mathrm{PbSO}}_4$.

So, Assertion is true while reason is false.