Chapter 8 - Sections 8.1-8.9 - Exercises - Problems by Topic - Page 376: 71

$O^{2-}$>$F^{-}$>$Ne$>$Na^{+}$>$Mg^{2+}$

These are isoelectronic speices, which means they all have the same number of electrons. However, they have diffrent number of protons. Having fewer protons results in a lesser pull on the electrons and therefore, a larger radius. Therefore, an increase in the atomic number determines the order of the decreasing radii.