For the octahedral complexes of $F{e}^{3+}$ in $SC{N}^{-}$ (thiocyanato-S) and in $C{N}^{-}$  ligand environments, the difference between the spin-only magnetic moments in Bohr magnetons (When approximated to the nearest integer) is [Atomic number of Fe = 26]

${\left[Fe{\left(SCN\right)}_6\right]}^{3-}$ and  ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$
In both the cases the electronic configuration of$F{e}^{3+}$   will be $1s^2,2s^2,2p^6,3s^2,3p^6,3d^5$ In ${\left[Fe{\left(SCN\right)}_6\right]}^{3-},\overline{S}CN$ is a weak field ligand and in ${\left[Fe{\left(CN\right)}_6\right]}^{3-},\overline{C}N$ is a strong field ligand, the pairing will occur only in case of  ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$
In  ${\left[Fe{\left(SCN\right)}_6\right]}^{3-}$

$\therefore \mu =\sqrt{n(n+2)}=\sqrt{5(5+2)}=\sqrt{35}=5.91BM$
In  ${\left[Fe{\left(CN\right)}_6\right]}^{3-},$

$\mu =\sqrt{n(n+2)}=\sqrt{1(1+2)}=\sqrt{3}=1.73BM$
Difference in spin only magnetic moment =  $5.91-1.73=4.18=4BM$