The equilibrium : 

 $2{\mathrm{Cu}}^{\mathrm{I}}\rightleftharpoons {\mathrm{Cu}}^0+{\mathrm{Cu}}^{II}$

in an aqueous medium, at 25° C shifts towards the left in the presence of :

Cu²⁺ combines with CN^- and SCN^- ions to generate ${\left[\mathrm{Cu}(\mathrm{CN}{)}_4\right]}^{3-}$  and  ${\left[\mathrm{Cu}(\mathrm{SCN}{)}_4\right]}^{3-}$, respectively. Here, the complete reactions are given as,

$\begin{array}{l}{\mathrm{Cu}}^{2+}+2{\mathrm{CN}}^{-}\to \mathrm{Cu}(\mathrm{CN}{)}_2\\ 2\mathrm{Cu}(\mathrm{CN}{)}_2\to 2\mathrm{CuCN}+(\mathrm{CN}{)}_2\\ \mathrm{CuCN}+3{\mathrm{CN}}^{-}\to {\left[\mathrm{Cu}(\mathrm{CN}{)}_4\right]}^{3-}\\ {\mathrm{Cu}}^{2+}+4{\mathrm{SCN}}^{-}\to {\left[\mathrm{Cu}(\mathrm{SCN}{)}_4\right]}^{2-}\end{array}$

Additionally, Cu²⁺ and  ${\mathrm{CuCl}}_2$ mix, and CuCl, which interacts with Cu to generate Cu, pushes the reaction in the other direction.

${\mathrm{CuCl}}_2+\mathrm{Cu}\to 2\mathrm{CuCl}\downarrow$

Thus, the options b, c, and d are correct.