How many of the following metal ions have similar value of spin...

From magnetic moment formula:
${\mu}_{s} = \sqrt{n ( n + 2 )}BM ( n =$ no. of unpaired electrons )

Ion E.C. n
${V}^{3 +}: [ Ar ] 3{d}^{2}4{s}^{0}2$

${Cr}^{3 +}: [ Ar ] 3{d}^{3}4{s}^{0}3$

${Fe}^{2 +}: [ Ar ] 3{d}^{6}4{s}^{0}4$

${Ni}^{3 +}: [ Ar ] 3{d}^{7}4{s}^{0}3$

Thus, ${Cr}^{3 +} \text{ and } {Ni}^{3 +}$ have same value of ${\mu}_{s}$