Question

Which of the following compounds is not coloured?

• A. $N{a}_2\left[CuC{l}_4\right]$
• B. $N{a}_2\left[CdC{l}_4\right]$
• C. $K_4\left[Fe(CN{)}_6\right]$
• D. $K_3\left[Fe(CN{)}_6\right]$

Answer 1

Answer: (B)

Oxidation state of

$Cu$ in $N{a}_2\left[CuC{l}_4\right]=+2$ i.e., $C{u}^{2+}\to 3d^9$

$Cd$ in $N{a}_2\left[CdC{l}_4\right]=+2$ i.e., $C{d}^{2+}\to 4d^{10}$

$Fe$ in $K_4\left[Fe(CN{)}_6\right]=+2$ i.e., $F{e}^{2+}\to 3d^6$

$Fe$ in $K_3\left[Fe(CN{)}_6\right]=+3$ i.e., $F{e}^{3+}\to 3d^5$

Since $Cd$ in $N{a}_2\left[CdC{l}_4\right]$ possesses completely filled $d$ -subshell, it is a colourless compound.