Which of the following has the smallest radius? Group of answer choices Ne Na+ Mg2+ F– O2–?

Refer to the table below.

All of the five given species are isoelectronic. Mg²⁺ has smallest radius because it has the greatest nuclear charge (the greatest number of protons) to attract the same number of electrons

Smallest is Mg2+

did you try googling ionic radius of the elements?
https://en.wikipedia.org/wiki/Ionic_radius