Consider the group 1A elements sodium (period 3), potassium (period 4), and rubidium (period 5). What would you predict about the ionization energies of these elements?

Ionization energies increase from left to right and down to up in a periodic table. The given elements are all group one elements so the ionization energy could be rank as Rb>K>Na. Hope this answers the question. Have a nice day.