Which of the following best explains why the Na^+ ion is larger than the Mg^{2+} ion?

• A. Mg^{2+} has a larger electron cloud than Na^+, making it larger in size.
• B. Na^+ has more electrons than Mg^{2+}, leading to a larger ionic radius.
• C. Na^+ and Mg^{2+} have the same number of protons, but Na^+ has a higher nuclear charge.
• D. Na^+ has fewer protons than Mg^{2+}, resulting in a weaker attraction between the nucleus and the electrons.

Answer: (D)

Verified step by step guidance

1. Identify the electron configuration of both ions: Na^+ and Mg^{2+} both have the same number of electrons because Na loses one electron and Mg loses two electrons, resulting in the electron configuration of neon (10 electrons) for both ions.
2. Recognize that since both ions have the same number of electrons, the difference in size is due to the number of protons (nuclear charge) in the nucleus attracting those electrons.
3. Note that Na^+ has 11 protons, while Mg^{2+} has 12 protons, meaning Mg^{2+} has a higher positive charge in the nucleus pulling the electron cloud closer.
4. Understand that a higher nuclear charge with the same number of electrons results in a stronger electrostatic attraction, which pulls the electrons closer to the nucleus, decreasing the ionic radius.
5. Conclude that Na^+ is larger than Mg^{2+} because Na^+ has fewer protons, leading to a weaker attraction between the nucleus and the electrons, allowing the electron cloud to be more spread out.