A) Ag
B) Cu
C) Al
D) Zn
Correct Answer: A
Solution :
Gold (Au) and silver (Ag) are extracted by treating their ores with dilute NaCN solution in the presence of air. During this process, a cyanide complex is formed which gives pure metal when treated with more electropositive metal like Zn. \[4\,Ag+8\,C{{N}^{-}}+2{{H}_{2}}O+{{O}_{2}}\] \[\xrightarrow{{}}\,4\,{{[Ag\,{{(CN)}_{2}}]}^{-}}+4O{{H}^{-}}\] \[2{{[Ag\,{{(CN)}_{2}}]}^{-}}+Zn\xrightarrow{{}}{{[Zn\,{{(CN)}_{4}}]}^{2-}}+\underset{silver}{\mathop{2\,Ag}}\,\] This process is called Mac Arthur Forest process.
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