KVPY SB SX Exam 2011 Question Paper

${\left[{\mathit{M}\mathit{n}}^{+2}{\left(\mathit{C}\mathit{N}\right)}_6\right]}^{-4}$
${\mathit{M}\mathit{n}}^{+2}\to 3{\mathit{d}}^{5}4{\mathit{s}}^{0}4\mathit{p}$
${\mathit{C}\mathit{N}}^{-}$is strong ligands so creates back paring effect of $\left(\mathit{n}-1\right)$ d orbitals configuration
So, unpaired ${\mathit{e}}^{-}=1$
$\mathit{\mu }=\sqrt{\mathit{n}\left(\mathit{n}+2\right)}$ B.M
$\mathit{\mu }=1.73$ B.M
And in ${\left[{\mathit{M}\mathit{n}\mathit{B}\mathit{r}}_4\right]}^{-2}$
Br is a weak ligands so no back pairing effect on $\left(\mathit{n}-1\right)$ d orbital so, unpaired ${\mathit{e}}^{-}$is $=5$
$\mathit{\mu }=\sqrt{5\left(5+2\right)}=\sqrt{35}=5.92$ B.M