Question

Extraction of gold (Au) involves the formation of complex ions X and Y.
$Gold \;ore\xrightarrow[{C{N^ - },{H_2}O,{O_2}}]{{roasting}}H{O^ - } + X\xrightarrow{{Zn}}Y + Au$
X and Y respectively are:
A. $Au(CN)_2^ -$ and $Zn(CN)_4^{2 - }$
B. $Au(CN)_4^{3 - }$ and $Zn(CN)_4^{2 - }$
C. $Au(CN)_3^ -$ and $Zn(CN)_6^{4 - }$
D. $Au(CN)_4^ -$ and $Zn(CN)_3^ -$

Answer 1

Hint: The given reaction is taking place in two steps, in the first step the reaction of gold is taking place with the cyanide ion to form a gold cyanide complex. In the second step, displacement of gold metal with zinc takes place.

Complete step by step answer:
The roasting is defined as the metallurgical process which is used to purify the metal components from its metal ore. The roasting process involves the gas-solid reaction taking place at high temperature.
The metal gold is extracted from its ore by the process of cyanidation. In the cyanidation process, the metallic gold is oxidized and dissolved in an alkaline solution of cyanide. After the gold is completely dissolved in the cyanide solution, the solution is separated from the solid.
The process involved in the extraction of gold is shown below.
$Gold \;ore\xrightarrow[{C{N^ - },{H_2}O,{O_2}}]{{roasting}}H{O^ - } + Au(CN)_2^ - \xrightarrow{{Zn}}Zn(CN)_4^{2 - } + Au$
In the process, the gold present in the ore first reacts with the cyanide ion to form a complex $Au(CN)_2^ -$. A single displacement reaction takes place where the complex $Au(CN)_2^ -$reacts with zinc metal where the zinc replaces the gold metal to form a complex $Zn(CN)_4^{2 - }$.
Thus, X is $Au(CN)_2^ -$and Y is $Zn(CN)_4^{2 - }$.
Therefore, the correct option is A.

Note:
 Don’t get confused by the charge of the metal as zinc is present in +2 oxidation state and gold has +1,to +3 oxidation state. In the extraction of higher content of gold from the gold metal ore, the cyanidation process is accompanied by a vat leaching process in which the slurry of ore and solvent is stored in large tanks with implanted agitator.