Question

The spin-only magnetic moment value for the complex $\left[Co\right(CN{)}_6{]}^{4-}$ is BM. [At. no. of Co = 27]

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Answer 1

In the given complex, oxidation state of $Co$ is +2.
Configuration of $C{o}^{2+}$ is $3d^{7}4s^2$
$C{N}^{-}$ is strong field ligand and cause pairing of electrons.
$\therefore$
$\left(t_{2}g{)}^6\right(e_g{)}^1$

Spin only magnetic moment $\left(\mu \right)=\sqrt{n(n+2)}BM$
n is number of unpaired electrons
$\mu =\sqrt{3}=1.732BM$