(A) Self-reduction reactions PbS + 2PbO → 3Pb+SO2 Cu2S+2Cu2O → 6Cu+SO2 (B) Carbon reduction reaction PbO + C → Pb + CO (C) Complex formation and displacement by metal Ag2S+4NaCN → 2Na[Ag(CN)2]+Na2S 2Na[Ag(CN)2]+Zn → 2Ag+Na2[Zn(CN)4] (D) Decomposition of iodide BI3 (heated under red hot tungsten) → B + 3I (iodide)