question_answer

                In which of the following pairs are both the ions coloured in aqueous solution?                 

A)                 \[N{{i}^{2+}},\,T{{i}^{3+}}\]                 \[_{28}Ni=1{{s}^{2}},2{{s}^{2}}\,2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{8}},4{{s}^{2}}\]                                 \[N{{i}^{2+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{{}}}\]                 \[_{22}Ti=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{2}},4{{s}^{2}}\]                                 \[T{{i}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}}\]                 \[_{21}Sc=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}},4{{s}^{2}}\]                 \[S{{c}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}\]                 (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, \[N{{i}^{2+}}\] and \[T{{i}^{3+}}\] ions are coloured ions in aqueous solution due to presence of unpaired electrons in d-sub-shell.

B)                 \[S{{c}^{3+}},\,T{{i}^{3+}}\]

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

D)                 \[N{{i}^{2+}},\,C{{u}^{+}}\]                 (At. no.: Sc = 21, Ti = 22, Ni = 28, Cu = 29, Co = 27)