Statues coated with white lead on long exposure to atmosphere turn black and the original colour can be restored on treatment with ${{H}_{2}}$${{O}_{2}}$. Explain

On long exposure to atmosphere, white lead gets changed to black lead sulphide by action of ${{H}{2}}S: <img src="/uploads/db3785/original/2X/9/9fabe6b611920062aede35ad48a9cd0402e39af2.png" width="342" height="65"> hence white statues are turned black. The treatment of statues with {{H}{2}}$${{O}{2}} changes black PbS into while PbS{{O}{4}}$ and hence the original white colour of statues in restored.