B. Cl; it takes much more energy to pull an electron away from a valence shell that is nearly full.
The correct answer is D. Mg; it takes more energy to pull two electrons away from magnesium (Mg) than it does to take them from chlorine (Cl). The ionization energy refers to the amount of energy required to remove an electron from an atom or ion in the gaseous state. Magnesium has a higher ionization energy because it has a higher number of protons in its nucleus, which results in a stronger attraction between the electrons and the nucleus. As a result, more energy is needed to remove electrons from magnesium compared to chlorine.
