Question

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

Explanation:

电离能是指在气态下从原子或离子中移除一个电子所需的能量。添加电子对应的是电子亲和能，且电离能定义中是气态而非液态。

Answer:

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