question_answer

In which of the following pairs are both the ions coloured in aqueous solution? (At. no. : Sc = 21, Ti = 22, Ni = 28, Cu = 29, Co =27)

A)  \[N{{i}^{2+}},T{{i}^{3+}}\]

B)  \[S{{c}^{3+}},T{{i}^{3+}}\]

C)  \[S{{c}^{3+}},C{{o}^{2+}}\]

D)  \[N{{i}^{2+}},C{{u}^{+}}\]

Correct Answer: A

Solution :

 \[_{28}Ni=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{8}},4{{s}^{2}}\] \[N{{i}^{2+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{8}}\]  (2 unpaired electrons) \[_{28}Ti=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{8}},4{{s}^{2}}\] \[T{{i}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}}\] (1 unpaired electron) \[_{21}Sc=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}},4{{s}^{2}}\] \[S{{c}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}\] (no unpaired electron) \[_{29}Cu=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}\] \[C{{u}^{+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}\] (no unpaired electron) Hence, in above ions,\[N{{i}^{2+}},\]and\[T{{I}^{3+}}\]ions are coloured ions in aqueous solution due to presence of unpaired electrons in d-subshell.