Cinnabar (HgS) and galena (PbS) on roasting give their respective metals but zinc blende does not. Explain.

Explanation

On roasting all these sulphide ores are partly converted into their respective oxides. Since the oxides of mercury and lead are unstable while that of zinc is stable, therefore, oxides of mercury and lead bring about the reduction of their respective sulphides to the corresponding metals but zinc oxide does not reduce ZnS to Zn metal.
`{:(HgS + 2HgO overset(Delta)rarr 3Hg + SO_(2)),(PbS + 2PbO overset(Delta)rarr 3Pb + SO_(2)),(ZnS + 2ZnO rarr 3Zn + SO_(2)):}`