Concept:By definition, first ionization energy is the energy required to remove one mole of electrons from one mole of
isolated gaseous atoms to form gaseous cations.
Formula:$$ X_{(g)} \longrightarrow X^+_{(g)} + e^- $$
Solution:- The definition strictly demands that the starting material is an isolated, single gaseous atom (\( \text{Br}_{(g)} \)), NOT a molecule.
- Option B shows exactly this: a single, gaseous Bromine atom losing one electron to become a gaseous Bromine cation.
Why other options are incorrect:- Option A, Option C, Option D: These involve \( \text{Br}_2 \) molecules (either gaseous or liquid). Ionizing a molecule involves bond dissociation enthalpy and/or enthalpy of vaporization, which confounds the pure definition of atomic ionization energy.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.