Oil paintings is blackened by atmospheric H2S due to the formation of X, H2O2, changes X to colourless (white) Y. X and Y respectively are

Oil paints contain Pb2+ in the form of CH3COO2Pb. In contact with atmospheric H2S, it is blackened due to the formation of PbS(X) .PbS can be cleaned by H2O2, which changes PbS to PbSO4, (Y)CH3COO2Pb(In oil paint) +H2S→PbSBlack  x+2CH3COOHPbS+4H2O2→PbSO4white  Y+H2O