Step 1: Understanding the Concept:
Ionization energy generally increases across a period (left to right) but shows anomalies at half-filled (\(p^3\)) and fully-filled (\(s^2\)) subshells due to extra stability.
Step 2: Detailed Explanation:
For \(n=2\) (Period 2 elements):
1. D (ns²np⁶): Neon (Noble gas). Highest IE due to stable octet \(\to\) 2080 (I).
2. C (ns²np³): Nitrogen. High IE due to half-filled p-orbital \(\to\) 1402 (IV).
3. A (ns²): Beryllium. Higher than Boron due to fully-filled s-orbital penetration \(\to\) 899 (II).
4. B (ns²np¹): Boron. Lower than Beryllium \(\to\) 800 (III).
Step 3: Final Answer:
A-II, B-III, C-IV, D-I.