question_answer

In which of the following pairs are both the ions coloured in aqueous solution? [AIPMT (S) 2006]

(At. no.: Sc = 21, Ti = 22, Ni = 28, Cu = 29, Co = 27)

A) Ni2+, Ti3+

B) Sc3+, Ti3+                    

C) Sc3 , Co2+

D) Ni2+, Cu+

Correct Answer: A

Solution :

[a] \[_{28}Ni=1{{s}^{2}},2{{s}^{2}}\,2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{8}},4{{s}^{2}}\]

\[N{{i}^{2+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{{}}}\]

\[_{22}Ti=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{2}},4{{s}^{2}}\]

\[T{{i}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}}\]

\[_{21}Sc=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}},4{{s}^{2}}\]

\[S{{c}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}\]

(unpaired electron in d-orbital is not possible)

\[_{29}Cu=1{{s}^{2}},2{{s}^{2}}\,2{{p}^{6}},3{{s}^{2}}\,3{{p}^{6}}\,3{{d}^{10}},4{{s}^{1}}\]

\[C{{u}^{+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}\]

(complete d-orbital)

Hence, in above ions, Ni2+ and Ti3+ ions are coloured ions in aqueous solution due to presence of unpaired electrons in d-sub-shell.