Question

Which best describes ionization energy?

Answer 1

A. energy needed to add an electron to a neutral atom in the gas phase
B. energy needed to add an electron to a neutral atom in the liquid phase
C. energy needed to remove an electron from an atom or ion in the gas phase
D. energy needed to remove an electron from an atom or ion in the liquid phase

Answer 2

The ionization energy (IE) is qualitatively defined as the amount of energy required to remove the most loosely bound electron of an isolated gaseous atom to form a cation.
https://en.wikipedia.org/wiki/Ionization_energy