Question

$CuS{O}_4$ decolourises on addition of excess KCN, the product is:

• A. $[CuCN{)}_4{]}^{2-}$
• B. $C{u}^{2+}$ get reduced to form $\left[Cu\right(CN{)}_4{]}^{3-}$
• C. $Cu(CN{)}_2$
• D. $CuCN$

Answer 1

The correct option is A $[CuCN{)}_4{]}^{2-}$

As $\left[Cu\right(CN{)}_4{]}^{2-}$ is diamagnetic in nature thereby not having unpaired $e^{-}$ for d-d transition to show color.

$C{u}^{2+}$ $4s^{0}3d^9$

(Refer to Image)

All $e^{-}s$ are paired as $CN$ is a strong ligand.