AP EAMCET Engineering 2013 Solved Paper

In the extraction of silver from cyanide process (also Mac-Arthur Forrest process), the siliver compound dissolve in NaCN solution forming a soluble complex salt, in presence of air, then silver is precipitated from this complex salt by the addition of Zn, because Zn being more reactive displaces the Ag.
Ag2S+4NaCN⇌2Na[Ag(CN)2] +Na2S↓
Na2S+2O2→Na2SO4
2Na[Ag(CN)2]+Zn→Na2[Zn(CN)4] +2Ag↓