Which of the following best defines the first ionization energy?

• A. The energy required to remove one electron from a neutral atom in its gaseous state.
• B. The energy required to remove all electrons from an atom.
• C. The energy needed to break a chemical bond in a molecule.
• D. The energy released when an electron is added to a neutral atom in its gaseous state.

Answer: (A)

Verified step by step guidance

1. Understand that ionization energy refers to the energy involved in removing electrons from atoms or ions.
2. Recall that the first ionization energy specifically means the energy required to remove the first (or outermost) electron from a neutral atom in the gaseous state.
3. Recognize that removing all electrons from an atom would refer to successive ionization energies, not just the first.
4. Note that breaking a chemical bond involves bond dissociation energy, which is different from ionization energy.
5. Remember that energy released when an electron is added to a neutral atom is called electron affinity, not ionization energy.