Concept:Across a period, ionization energy generally increases, but half-filled subshells provide an anomalous boost in stability and thus a higher ionization energy.
Formula:$$ \text{IE Trend: Be} < \text{C} < \text{O} < \text{N} $$
Solution:- Carbon, Nitrogen, and Oxygen are in Period 2. Generally, IE increases left to right.
- Nitrogen has a perfectly half-filled \( 2p^3 \) valence shell, which is highly symmetrically stable.
- Oxygen has a \( 2p^4 \) shell. The pairing of electrons in one p-orbital causes repulsion, making it easier to remove one electron from Oxygen than from the stable Nitrogen.
- Thus, Nitrogen has a higher IE than Oxygen, making it the highest among the choices.
Why other options are incorrect:- Option A, Option B, Option D: Lack the extraordinary stability of a half-filled p-subshell combined with high nuclear charge.
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