Describe the role of
(i) `NaCN` in the extraction of gold from gold ore.
(ii) `SiO_(2)` in the extraction of copper from copper matter. (iii) Iodine in the refining of zirconium.
Write chemical equations for the involved reactions.

Explanation

(i) Role of NaCN in the extraction of gold is to do leaching of gold ore in the pressence of air from which the gold is obtained later by replacement.
`4Au(s)+8CN^(-)(aq)+2 H_(2)O+O_(2)(g) rightarrow 4[Au(CN)_(2)]^(-)+4 OH^(-)`
(ii) `SiO_(2)` is added in copper matter to convert the remaining FeS, FeO to slag
`FeO+Si O_(2) rightarrow underset(("slag")) (Fe Si O_(3))`
(iii) Iodine is heated with Zirconium to form a volatile-compound which on further heating decompose to give pure zirconium
`Zr(impure)+2 I_(2)rightarrowZr I_(4)`
`Zr I_(4) rightarrow Zr(pure)+2 I_(2)`