Identify the metal ions among Co^ 2+ , Ni^ 2+ , Fe^ 2+ , V^ 3+ and...

The spin-only magnetic moment is given by $\mu = \sqrt{n(n+2)}$ BM, where $n$ is the number of unpaired electrons.
For $\mu > 3.0$ BM, $n$ must be $\ge 3$ (since for $n=2$, $\mu = \sqrt{8} \approx 2.83$ BM and for $n=3$, $\mu = \sqrt{15} \approx 3.87$ BM).
Electronic configurations and unpaired electrons ($n$) in high spin octahedral complexes:

Metal Ion	Configuration	$n$	$\mu$ (BM)
$Co^{2+}$	$[Ar] 3d^7$	3	3.87
$Ni^{2+}$	$[Ar] 3d^8$	2	2.83
$Fe^{2+}$	$[Ar] 3d^6$	4	4.90
$V^{3+}$	$[Ar] 3d^2$	2	2.83
$Ti^{2+}$	$[Ar] 3d^2$	2	2.83

The metal ions with $\mu > 3.0$ BM are $Co^{2+}$ ($n=3$)$and Fe^{2+}$ ($n=4$).
The sum of unpaired electrons for these ions is $3 + 4 = 7$.