question_answer

Which one of the following ions will give a coloured solution?

A)  \[C{{u}^{+}}\]   

B)  \[F{{e}^{2+}}\]

C)  \[Z{{n}^{2+}}\]  

D)  \[A{{g}^{+}}\]

Correct Answer: B

Solution :

Presence of unpaired d-electrons is an essential condition to give colour. [a] \[C{{u}^{+}}=[Ar]\,3{{d}^{10}}\] (No unpaired electron) [b] \[F{{e}^{2+}}=[Ar]\,3{{d}^{6}}4{{s}^{0}}\] (Four unpaired electrons) [c] \[Z{{n}^{2+}}=[Ar]\,3{{d}^{10}}4{{s}^{0}}\] (No unpaired electron) [d] \[A{{g}^{+}}=[Xe]\,4{{d}^{10}}\] (No unpaired electron) Hence, only \[F{{e}^{2+}}\] will give a coloured solution.