Concept: Noble gas notation simplifies electronic configurations by replacing inner, fully filled shells with the bracketed symbol of the preceding noble gas.
Formula: None required.
Solution: - Sodium (Na) has an atomic number \( Z = 11 \).
- The nearest preceding noble gas is Neon (Ne), which has \( Z = 10 \).
- Neon's configuration perfectly covers the core electrons: \( 1s^2, 2s^2, 2p^6 \).
- Sodium has one remaining valence electron (\( 11 - 10 = 1 \)).
- This final electron enters the next available energy level, which is the \( 3s \) orbital.
- The condensed configuration is therefore \( \text{[Ne]} 3s^1 \).
Why other options are incorrect: Option B represents Magnesium (\( Z=12 \)). Option C represents a Sodium ion (\( \text{Na}^+ \)). Option D implies too many electrons.
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.