Question

Which of the following compounds is not coloured?

• A. $Na_{2}\lbrack CuCl_{4}\rbrack$
• B. $Na_{2}\lbrack CdCl_{4}\rbrack$
• C. $K_{4}\lbrack Fe(CN)_{6}\rbrack$
• D. $K_{3}\lbrack Fe(CN)_{6}\rbrack$

Answer 1

Answer: (B)

$Na_{2}\lbrack CdCl_{4}\rbrack$

Answer 2

$Na_{2}\lbrack CuCl_{4}\rbrack$ Cu = +2 or $Cu^{2 +} \rightarrow 3d^{9}$

$Na_{2}\lbrack CuCl_{4}\rbrack$ Cd = +2 or $Cd^{2 +} \rightarrow 4d^{10}$

$K_{4}\lbrack Fe(CN)_{6}\rbrack$ Fe = +2 or $Fe^{2 +} \rightarrow 3d^{6}$

$K_{3}\lbrack Fe(CN)_{6}\rbrack$ Fe = +3 or $Fe^{3 +} \rightarrow 3d^{5}$

Since $Cd^{2 +}$ has completely filled d-subshell hence it is colourless.