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:

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.