the ionization energy for iodine(I) is about twice that for rubidium (RB) even though they are both in the?

the ionization energy for iodine(I) is about twice that for rubidium (RB) even though they are both in the same period. the reason for this difference in their ionization energies is that an atom of iodine.
1has a radius that is about twice that of rubidium
2has seven electron in its outermost energy level whereas rubidium has only one
3has twice as many electrons in its outermost energy levelas compared to rubidium
4cannot achieve a stable electron configuration