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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 :

1. [Au(CN 4 ] – and [Zn(CN) 2 (OH 2 ] 2–
2. [Au(CN 2 ] – and [Zn (OH 4 ] 2–
3. [Au(CN 2 ] – and [Zn(CN) 4 ] 2–
4. [Au(CN 4 ] 2– and [Zn(CN) 6 ] 4–

Correct answer: [Au(CN 2 ] – and [Zn(CN) 4 ] 2–

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