Chemistry- ionic radii of Mg and Na?

Question

Na has ionic radius of 0.157 nm. Mg has radius of 0.136nm. Why is the Mg atom smaller?

Answer 1

Because Mg2+ has 12 protons in the nucleus, Na+ has less, only 11. The outer shell for both ions is L (n = 2), but more protons result in stronger force from the nucleus to the outer shell's electron, so smaller ionic radius.