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Question

Chemistry Question on d -and f -Block Elements

Copper sulphate dissolves in excess of KCN to give

A

CuCNCuCN

B

[Cu(CN)4]3−[Cu(CN)_4]^{3-}

C

[Cu(CN)4]2−[Cu(CN)_4]^{2-}

D

Cu(CN)2Cu(CN)_2

Answer

[Cu(CN)4]3−[Cu(CN)_4]^{3-}

Explanation

Solution

2KCN+CuSO4→K2SO4+Cu(CN)22 KCN + CuSO _{4} \rightarrow K _{2} SO _{4}+ Cu ( CN )_{2}
Cu(CN)2unstable→CuCN+(CN)2\underset{\text{unstable}}{{Cu(CN)_2}} \to CuCN +(CN)_2
CuCN+3KCN→K3[Cu(CN)4]CuCN +3 KCN \to K _{3}\left[ Cu ( CN )_{4}\right]

i.e. [Cu(CN)4]3−\left[ Cu ( CN )_{4}\right]^{3-}