The magnetic moment is measured in Bohr Magneton (BM). Spin only...

The spin only magnetic moment can be calculated as follows

$\mu = \sqrt{n\left(n + 2\right)}BM$

$n =$Number of unpaired electrons

${\left[Fe{\left({H}_{2}O\right)}_{6}\right]}^{3 +} = {d}^{5} ( Highspincomplex ) = 5$.unpaired electrons
$\mu = \sqrt{5 \times 7} = \sqrt{35}$
$= 5 . 92B . M .$
${\left[Fe{\left(CN\right)}_{6}\right]}^{3 +} = {d}^{5} ( Lowspincomplex ) = 1$
$\mu = \sqrt{1 \times 3} = \sqrt{3}$
$= 1 . 732B . M .$