# Which of the following has the maximum number of unpaired electrons?

$Mg^{2+}\qquad(c)\;Ti^{3+}\qquad(c)\;V^{3+}\qquad(d)\;Fe^{2+}$

$Fe^{2+}$ has $1s^2,2s^22p^6,3s^23p^63d^6$ configuration with 4 unpaired electron.
Hence (d) is the correct answer.