The magnetic moment of a transition metal compound has been calculated to be 3.87 B.M. The metal ion is

$$ \begin{aligned} & \mathrm{Cr}^{+2}:[\mathrm{Ar}], 3 \mathrm{~d}^4, 4 \mathrm{~s}^0 \mathrm{n}=4, \mu=\sqrt{4(4+2)}=\sqrt{24} =4.89 \mathrm{BM} \\\\ & \mathrm{Mn}^{+2}:[\mathrm{Ar}], 3 \mathrm{~d}^5, 4 \mathrm{~s}^0 \mathrm{n}=5, \mu=\sqrt{5(5+2)}=\sqrt{35} =5.91 \mathrm{BM} \\\\ & \mathrm{V}^{+2}:[\mathrm{Ar}], 3 \mathrm{~d}^3, 4 \mathrm{~s}^0 \mathrm{n}=3, \mu=\sqrt{3(3+2)}=\sqrt{15} =3.87 \mathrm{BM} \\\\ & \mathrm{Ti}^{+2}:[\mathrm{Ar}], 3 \mathrm{~d}^2, 4 \mathrm{~s}^0 \mathrm{n}=2, \mu=\sqrt{2(2+2)}=\sqrt{8} =2.82 \mathrm{BM} \end{aligned} $$