Answer:
The process of the first ionization energy
Step-by-step explanation:
The ionization energy is the energy required to remove one electron for one isolated atom at the gas phase. The first electron to be removed is the valence electron which is far away from the nuclei. Because of that, this electron suffers a less attraction force.
For the second ionization energy, the electron will be closer to the nuclei, so it is more attracted, then a large amount of energy is necessary to remove it. For the third, the amount of energy will be larger. So, the first ionization energy requires the least amount of energy.