Which equation correctly represents the third ionization energy (I_3) of lithium?

• A. Li^{3+} (g) → Li^{4+} (g) + e^{-}
• B. Li^{+} (g) → Li^{2+} (g) + e^{-}
• C. Li^{2+} (g) → Li^{3+} (g) + e^{-}
• D. Li (g) → Li^{+} (g) + e^{-}

Answer: (C)

Verified step by step guidance

1. Understand that the third ionization energy (I_3) refers to the energy required to remove the third electron from an atom or ion in the gas phase.
2. Recall the sequence of ionization energies: the first ionization energy (I_1) removes the first electron from the neutral atom, the second ionization energy (I_2) removes the second electron from the resulting +1 ion, and the third ionization energy (I_3) removes the third electron from the +2 ion.
3. Write the general form of the third ionization energy reaction as the removal of an electron from the +2 charged ion: \(\mathrm{Li^{2+} (g) \rightarrow Li^{3+} (g) + e^{-}}\).
4. Compare this with the given options and identify that the correct equation must start with \(\mathrm{Li^{2+} (g)}\) and produce \(\mathrm{Li^{3+} (g)}\) plus an electron.
5. Confirm that the other options either represent the first or second ionization steps or an impossible ionization state (like \(\mathrm{Li^{4+}}\)), so they do not correctly represent the third ionization energy.