JEE Main 2022 · 25 Jun · Shift 1 · Chemistry Q64

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ChemistrySingle correct+4 / -1Question 64 of 90

Leaching of gold with dilute aqueous solution of 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 :

\mathrm{[Au(CN)_4]^-}

and

\mathrm{[Zn(CN)_2(OH)_2]^{2-}}

\mathrm{[Au(CN)_2]^-}

and

\mathrm{[Zn(OH)_4]^{2-}}

\mathrm{[Au(CN)_2]^-}

and

\mathrm{[Zn(CN)_4]^{2-}}

\mathrm{[Au(CN)_4]^{2-}}

and

\mathrm{[Zn(CN)_6]^{4-}}

Answer and worked solution

Official answer: C

Leaching. $\mathrm{4Au+8CN^-+2H_2O+O_2\rightarrow4[Au(CN)_2]^-+4OH^-}$ .

Displacement. $\mathrm{2[Au(CN)_2]^-+Zn\rightarrow[Zn(CN)_4]^{2-}+2Au}$ .

(C)

Topics:Extraction of specific metals Stability and applications

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JEE Main 2022 · 25 Jun · Shift 1, Chemistry question 64