question_answer

                The number of unpaired electrons in me complex ion \[{{[Co{{F}_{6}}]}^{3-}}\] is:                                               

A)                 4                             

B)                 zero       

C)                 2                             

D)                 3                 (Atomic number Co = 27)

Correct Answer: A

Solution :

                In complex ion \[{{[Co{{F}_{6}}]}^{3-}}\,,\,Co\] is present at +3 oxidation state                  \[\begin{align}   & _{27}Co=1{{s}^{2}},2{{s}^{2}}\,2{{p}^{6}},\,3{{s}^{2}}3{{p}^{6}}\,3{{d}^{7}},4{{s}^{2}} \\  & C{{o}^{3+}}=1{{s}^{2}},2{{s}^{2}}\,2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}\,3{{d}^{6}} \\ \end{align}\]                                 Thus, the number of unpaired electrons in 3d sub-shell of \[{{[Co{{F}_{6}}]}^{3-}}\] is 4