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  • Leaching of gold with dilute aqueous solution of in presence of oxygen gives complex [A], which

Leaching of gold with dilute aqueous solution of \mathrm{NaCN} in presence of oxygen gives complex [A], which on reaction with Zinc forms the elemental gold and another complex [B]. [A] and [B] respectively are :

Option: 1

\begin{aligned} &{\left[\mathrm{Au}(\mathrm{CN})_{4}\right]^{-} \text {and }\left[\mathrm{Zn}(\mathrm{CN})_{2}(\mathrm{OH})_{2}\right]^{2-}} \\ \end{aligned}


Option: 2

\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-} \text {and }\left[\mathrm{Zn}(\mathrm{OH})_{4}\right]^{2-}


Option: 3

\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-} \text {and }\left[\mathrm{Zn}(\mathrm{CN})_{4}\right]^{2-}


Option: 4

\left[\mathrm{Au}(\mathrm{CN})_{4}\right]^{2-}$ and $\left[\mathrm{Zn}(\mathrm{CN})_{6}\right]^{4-}


Answers (1)

best_answer

Leaching of Gold occurs as

\mathrm{Au}+\mathrm{CN}^{-}+\mathrm{O}_{2} \rightarrow \underset{\mathrm{[A]}}{\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}}+\mathrm{OH}^{-}

\left[\mathrm{A u(C N)_{2}}\right]^{-}\mathrm{+Z{n} \rightarrow A u+}\underset{\mathrm{[B]}}{\left[\mathrm{Z{n}}(\mathrm{CN})_{4}\right]^{2-}}

Thus, the complexes \mathrm{[A]} and \mathrm{[B]} are respectively \mathrm{[Au(CN)_2]^-} and \mathrm{[Zn(CN)_4]^{2-}}

Hence, the correct answer is Option (3)

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