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Copper sulphate on treatment with excess of KCN forms complex K3[Cu(CN)4] or [Cu(CN)4]3-. Which of the following reactions is correct?

1. CuSO4 + 2 KCN → Cu(CN)2 + K2SO4
2. Cu(CN)2 → Cu2(CN)2 + (CN)2
3. Cu2(CN)2 + 3 KCN → K3[Cu(CN)4] + CuCN
4. CuSO4 + 4 KCN → K3[Cu(CN)4] + CuCN

Correct answer: CuSO4 + 4 KCN → K3[Cu(CN)4] + CuCN

Solution

Copper sulfate reacts with excess potassium cyanide to form the complex K3[Cu(CN)4] along with CuCN as a byproduct. This matches the reaction in option D.

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