For the octahedral complexes of `Fe^(3+)` is `SCN^(-)` ( thiocyanato-S) and in `CN^(-)` 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]

Answer

4

Explanation

Fe(26) = `3d^(6)4s^(2), Fe^(3+)=3d^(5)`
In `[Fe(CN)_(6)]^(3-), CN^(-)` is a strong field ligand which causes pairing of electrons

`mu=sqrt(n(n+2))=sqrt(1(1+2))=sqrt(3)=1.732` BM
In `[Fe(SCN)_(6)]^(3-), SCN^(-)` being a weak field ligand does not cause pairing of electrons

`mu=sqrt(n(n+2))=sqrt(5(5+2))=sqrt(35)=5.916` BM
Difference = 5.916 - 1.732 = 4.184 `-=` 4 BM