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  4. The spin-only magnetic moment value for the complex [ Co ( CN )6]4- is B M. [At. no. of Co =27 ]

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Q. The spin-only magnetic moment value for the complex $\left[ Co ( CN )_{6}\right]^{4-}$ is_______ $B M$. [At. no. of $Co =27$ ]

JEE MainJEE Main 2021Coordination Compounds

Solution:

$\left[ Co ( CN )_{6}\right]^{4-}$
$x+6 \times(-1)=-4$
$x=+2 $
$Co ^{2+}:[ Ar ] 3 d^{7}$
and $C N^{-}$is a strong field ligand which can pair electron of central atom.
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It has one unpaired electron $(n)$ in $4 d$-subshell.
So spin only magnetic moment $(\mu)=\sqrt{n(n+2)}$ B.M
where $n=$ number of unpaired electrons.
$\mu=\sqrt{3}$ B.M
$\mu=1.73 \,B M$