Question

The number of unpaired electrons in the complex ion $\left[ CoF _{6}\right]^{3-}$ is
(At. no. of $Co =27$ )

• A. 3
• B. 2
• C. 4
• D. 0

Answer 1

Answer: (C)

In complex ion $\left[ CoF _{6}\right]^{3-}, Co$ is present in $+3$ oxidation state
${ }_{27} Co =1 s^{2}, 2 s^{2} \,2 p^{6}, 3 s^{2} \,3 p^{6} \,3 d^{7}, 4 s^{2} $
$ Co ^{3+}=1 s^{2}, 2 s^{2} \,2 p^{6}, 3 s^{2} \,3 p^{6} \,3 d^{6}$
Therefore, the number of unpaired electrons in $3 d$ subshell of $\left[ CoF _{6}\right]^{3-}$ is $4$ .