Ionization energy is the amount of energy necessary to

I think ionization energy is the energy required to remove an electron from a neutral atom. It is the amount of energy that is required to remove the most loosely bound electron, the valence electron, of an isolated gaseous atom to form a cation. Atoms and molecules have this measurement, which refer to the energy it takes for all atoms in one mole of a substance to each lose one electron.

The answer will be d