Arrange this isoelectronic series in order of decreasing radius: O2-, F-, Na+, Mg2+.

Verified step by step guidance

1. Identify that isoelectronic species have the same number of electrons. In this case, each species has 10 electrons.
2. Recognize that the size of isoelectronic species is influenced by the nuclear charge (number of protons). The more protons, the stronger the attraction to the electrons, and the smaller the radius.
3. List the atomic numbers (number of protons) for each species: O (8), F (9), Na (11), Mg (12).
4. Arrange the species in order of increasing nuclear charge: O^{2-} (8 protons), F^{-} (9 protons), Na^{+} (11 protons), Mg^{2+} (12 protons).
5. Order the species by decreasing radius, which is the reverse of increasing nuclear charge: O^{2-}, F^{-}, Na^{+}, Mg^{2+}.