Which best describes ionization energy? energy needed to add an electron to a neutral atom in the gas phase energy needed to add an electron to a neutral atom in the liquid phase energy needed to remove an electron from an atom or ion in the gas phase energy needed to remove an electron from an atom or ion in the liquid phase

Answer: energy needed to remove an electron from an atom or ion in the gas phase.

Explanation:

That is the very definition of ionization energy: ionization energy is the energy needed to remove (get appart) an electron from a neutral atom or ion in gas phase.

To form a positive ion one electron must be removed from a neutral atom. This process requires energy to overcome the attractive electrostatic force between the electron and the protons in the nucleus.

The energy needed to remove the first electron (from the neutral atom) is called first ionization energy. After this electron removal, the atom becomes ion, from which it is possible to remove additional electrons. The energy needed to remove a second electron is called second ionization energy. The energy needed to remove a third electron is called third ionization energy, and so on.

It is always harder to remove a third electron than the second, and it is harder to remove the second than the first one. So, the third ionization energy is greater than the second ionization energy, and this is greater than the first ionization energy.

Ionization energy is the energy needed to remove an electron from an atom or ion in a gas phase. The atom will become a cation and has an excess of proton, thus it will be positively charged. Ionization energy usually removes the most loosely bound valence electron.