Final answer:
Removing an electron from a neutral atom requires the most energy due to the strong electrostatic attraction between the electron and the nucleus.
Step-by-step explanation:
Removing an electron from a neutral atom requires the most energy. This is because the positive charge of the nucleus attracts the negatively charged electrons. When an electron is removed from a neutral atom, there is a strong electrostatic attraction between the electron and the nucleus. This attraction requires a significant amount of energy to overcome.