1) Metals at the bottom of the activity series are often found in free state.
2) The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.
3) When cinnabar (HgS) is heated in air, it is converted into HgO, then reduced to mercury on further heating.
4) Displacement from aqueous solution : When Ag2S is dissolved in KCN solution, it forms dicyanoargentate ions. When these ions are treated with Zn dust powder then Ag is precipitated.
Eg : Ag2S + 4 CN → 2 [Ag(CN)2] + S2-
2 [Ag(CN)2]-(aq) + Zn(S) → [Zn(CN)4]2- (aq)+ 2 Ag(s)
