Chemistry

Question Analysis
This question involves recalling a key experimental detail in the definition of first ionization energy. The main focus is on identifying the correct physical state for measuring ionization energy.

Key Concept Explanation
Ionization energy is defined as the energy required to remove a valence electron from a neutral gaseous atom.
Measuring in the gaseous state ensures that atoms are isolated and not influenced by intermolecular forces from neighboring atoms (which would affect the energy required to remove an electron).

Step-by-Step Solution
1. Recall the formal definition of first ionization energy.
2. Identify t...