Chemistry - Complete d-block Question with Solution | TestHub

The correct option is (B).

The spin-only magnetic moment depends entirely on the number of unpaired electrons ($n$) present in the ion's d-subshell.

The electronic configuration of Co³⁺ ($Z=27$) is $[Ar]3d^6$, which contains 4 unpaired electrons.

The electronic configuration of Fe²⁺ ($Z=26$) is also $[Ar]3d^6$, which similarly contains 4 unpaired electrons.

Since both ions share the same number of unpaired electrons ($n=4$), they have the exact same magnetic moment value ($\sqrt{4(4+2)}=\sqrt{24}BM$).