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).     JEE Main Online Paper (Held On 07 May 2012)

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 :

                Since \[C{{o}^{3+}}\] has lowest no. of unpaired electrons hence lowest paramagnetic behaviour is shown by \[{{[Co{{({{H}_{2}}O)}_{6}}]}^{2+}}\]