Rb
Of course Li, it is smallest ion which may exists in crystal lattice.
Fluorine has the largest first ionization energy among the halogens.
Lithium has the least number of protons, rubidium has the most number of protons.
As an example potassium has a lower first ionization energy than aluminum (Al).
The ionization energy of fluorine is 1681 kJ/mol (the first) and the ionization energy of iodine is 1008,4 kJ/mol.
Sodium
T he smallest first ionization energyis for lithium.
Helium has the highest ionization energy.
Fluorine has the largest first ionization energy among the halogens.
Lithium has the least number of protons, rubidium has the most number of protons.
Potassium has a higher ionization energy than cesium.
K :Apex
As an example potassium has a lower first ionization energy than aluminum (Al).
Ionization energy decrease down the group.So in halogens,Fluorine has highest 1st ionization energy.
As an example potassium has a lower first ionization energy than aluminum (Al).
Na, sodium
xenon increases from left to right across periods (first ionization energy)
Barium has more energy levels. So it has lesser ionization energy.