question_answer

Which of the following pairs is coloured in aqueous solution?

A) \[S{{c}^{3+}},C{{o}^{2+}}\]

B) \[N{{i}^{2+}},C{{u}^{+}}\]

C) \[N{{i}^{2+}},T{{i}^{3+}}\]

D)  \[S{{c}^{3+}},T{{i}^{3+}}\]

Correct Answer: C

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] \[_{22}Ti=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{2}}4{{s}^{2}}\] \[T{{i}^{3+}}=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{1}}\] [1 unpaired electron]  Hence, \[N{{i}^{2+}}\]and \[T{{i}^{3+}}\]are coloured in aqueous solution due to the presence of unpaired electrons in d-subshell.