question_answer

The aqueous solution containing which one of the following ions will be colourless? (Atomic no. Sc = 21, Fe = 26, Ti = 22, Mn = 25)

A)  \[S{{c}^{3+}}\] 

B)         \[F{{e}^{2+}}\]

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

D)         \[M{{n}^{2+}}\]

Correct Answer: A

Solution :

\[{}_{21}Sc=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}},4{{s}^{2}}\] So,          \[S{{c}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}\] (It is colourless due to absence of unpaired electrons in d-subshell) \[{}_{26}Fe=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{6}},4{{s}^{2}}\] \[F{{e}^{2+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{6}}\] (It is coloured due to presence of four unpaired electrons in d-subshell.) \[{}_{22}Ti=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{2}},4{{s}^{2}}\] \[T{{i}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{1}}\] (It is coloured due to presence   of one unpaired electron in d-subshell.) \[{}_{25}Mn=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{5}},4{{s}^{2}}\] \[M{{n}^{2+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{5}}\] (It is coloured due to presence of five unpaired electrons in d-subshell.)