Which equation represents the second ionization energy of magnesium?

• A. Mg^+ (g) → Mg^{2+} (g) + e^-
• B. Mg (s) → Mg^+ (g) + e^-
• C. Mg^{2+} (g) → Mg^{3+} (g) + e^-
• D. Mg (g) → Mg^+ (g) + e^-

Answer: (A)

Verified step by step guidance

1. Understand that ionization energy refers to the energy required to remove an electron from an atom or ion in the gas phase.
2. Recall that the first ionization energy is the energy needed to remove the first electron from a neutral atom, represented as: \(Mg (g) \rightarrow Mg^{+} (g) + e^{-}\).
3. The second ionization energy is the energy required to remove a second electron, but this time from the already singly charged ion, so it involves the reaction: \(Mg^{+} (g) \rightarrow Mg^{2+} (g) + e^{-}\).
4. Recognize that the other options either represent the first ionization energy (removal from neutral Mg) or an ionization beyond the second (such as \(Mg^{2+} \rightarrow Mg^{3+}\)), which is not the second ionization energy.
5. Therefore, the correct equation for the second ionization energy of magnesium is the one showing the removal of an electron from \(Mg^{+} (g)\) to form \(Mg^{2+} (g)\).