Concept:Within the same period, atomic radius decreases from left to right due to increasing effective nuclear charge drawing the electron cloud inward.
Formula:$$ \text{Radius Trend (Period 3): Na} > \text{Mg} > \text{P} > \text{S} $$
Solution:- All listed elements belong to Period 3 (they all have 3 electron shells).
- Sodium is in Group 1, Mg in Group 2, P in Group 15, and S in Group 16.
- Sulfur is the furthest right. Its nucleus has 16 protons, exerting the strongest electrostatic pull on the 3rd electron shell, compressing it to the smallest radius among the options.
Why other options are incorrect:- Option A, Option C, Option D: These elements have fewer protons pulling on the same 3rd shell, resulting in larger, less compressed radii.
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