The d- and f-Block Elements

Spin-only moment depends on unpaired electrons: $\mathrm{Ti^{3+}}$ ($d^1$) 1, $\mathrm{Cr^{2+}}$ ($d^4$) 4, $\mathrm{Mn^{2+}}$ ($d^5$) 5, $\mathrm{Fe^{2+}}$ ($d^6$) 4, $\mathrm{Sc^{3+}}$ ($d^0$) 0. B and D both have 4 unpaired electrons, $\mu = \sqrt{24} \approx 4.9$ BM.