question_answer

The d-electron configurations of \[C{{r}^{2+}},M{{n}^{2+}},F{{e}^{2+}}\] and \[C{{o}^{2+}}\] are \[{{d}^{4}},{{d}^{5}},{{d}^{6}}\] and \[{{d}^{7}}\] respectively. Which one of the following will exhibit the lowest paramagnetic behaviour? (Atomic no. Cr = 24, Mn = 25, Fe= 26, Co = 27).

A) \[{{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}\]        

B) \[{{[Cr{{({{H}_{2}}O)}_{6}}]}^{2+}}\]

C) \[{{[Mn{{({{H}_{2}}O)}_{6}}]}^{2+}}\]       

D) \[{{[Fe{{({{H}_{2}}O)}_{6}}]}^{2+}}\]

Correct Answer: A

Solution :

[a]

	Electronic configuration	No. of unpaired electrons
\[C{{o}^{2+}}\]	\[{{d}^{7}}\]	3
\[C{{r}^{2+}}\]	\[{{d}^{4}}\]	4
\[M{{n}^{2+}}\]	\[{{d}^{5}}\]	5
\[F{{e}^{2+}}\]	\[{{d}^{6}}\]	4

\[\therefore \]  Since \[C{{o}^{2+}}\] has lowest no. of unpaired electrons hence lowest paramagnetic behaviour is shown by \[{{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}\]