Pb and Sn are extracted from their chief ore by

PbO and PbSO4 get reduced by PbS itself which is already present in mixture because the reduction took place by the mixture itself, hence it is known as self-reduction.2PbO+PbS⟶Δ3Pb+SO2↑PbSO4+PbS⟶Δ2Pb+2SO2↑The process of extracting a metal by reduction of its oxide with carbon is called carbon reduction.SnO2+C→Sn+COSnO2+2CO→Sn+2CO2