Rb, Na, As, Li here. Lithium only has 3 electrons...can\'t have a 6th ionizationenergy, it is correct. the 1st ionization of Rb < Na , therefore the6th would be less as well. it is also correct. now, Arsenic has the highest 1st ionization of all. So the answer is As. Solution Rb, Na, As, Li here. Lithium only has 3 electrons...can\'t have a 6th ionizationenergy, it is correct. the 1st ionization of Rb < Na , therefore the6th would be less as well. it is also correct. now, Arsenic has the highest 1st ionization of all. So the answer is As..