Which of the following complex compounds is not coloured 

 $$\begin{gathered} {\mathrm{Na}}_2\left[{\mathrm{CdCl}}_4\right] \\ \mathrm{Cd} : 4{\mathrm{d}}^{10} 5{\mathrm{s}}^2 \end{gathered}$$

           ${\mathrm{Cd}}^{+2 }: 4{\mathrm{d}}^{10}$

Because there is no opportunity for d-d transition in Cd²⁺ ion, it lacks color.