$\mathrm{CuSO}_4$ decolourises on addition of $\mathrm{KCN}$, the product is

• A

  $\left[\mathrm{Cu}(\mathrm{CN})_4\right]^{2-}$
• B

  $\mathrm{Cu}^{2+}$ get reduced to form $\left[\mathrm{Cu}(\mathrm{CN})_4\right]^{3-}$
• C

  $\mathrm{Cu}(\mathrm{CN})_2$
• Correct answer
  D

  $\mathrm{CuCN}$

Solution

$\mathrm{CuSO}_4$ decolourise on addition of $\mathrm{KCN}$, the product is $\mathrm{CuCN}$ along with $(\mathrm{CN})_2$ but in excess of KCN is form colourless potassium tetra cyano cuperate (I)

Hence, the correct answer is option: 'D'.