Which elements on the periodic table have the highest ionization energies?

This question is without options and hence appears incomplete considering the structure of the question

Explanation:

Ionization energy is the minimum amount of energy required to remove a valence electron from an atom in its gaseous state. It requires lesser energy for an electron to be lost on the outermost shell than for two electrons to be lost on the same shell, hence ionization energy increases across the period since number of electrons increases across a period (making the amount of energy required to remove these electrons higher).

However, the closer valence electrons are to the central nucleus, the more difficult/energy required to remove such electrons hence ionization energy decreases down the group (since the more you go down the group, the farther the valence electrons are from the central nucleus).

1. Argon

2. Flourine

3. Neon

4. Helium