Valence shell electrons are taken out first, followed by inner shell electrons. If we take this into account, then${\mathrm{Mn}}^{3+}$ ,${\mathrm{Fe}}^{3+}$ , ${\mathrm{Co}}^{3+}$, and ${\mathrm{Ni}}^{3+}$, respectively, have 4,5,4,3, and 3, unpaired electrons. Fe 3+ therefore has the most unpaired electrons.