Answer:
D. Third ionization energy
Explanation:
Ionization energy describes the energy enough to remove the valence electrons from atoms in a ground state. It is a measure of the readiness of an atom to lose an electron. The lower this value, the easier it is for an atom to lose electrons and vice versa.
The first ionization energy is the energy needed to remove the most loosely bound electron of an atom. The third ionization energy would be the energy required to remove the third electron from an atom.
