Classification of Elements and Periodicity
Modern periodic table, periodic trends in radii, ionisation enthalpy, electron gain enthalpy and electronegativity.
In the official syllabus: IAPT — Syllabus for National Standard Examination and Indian National Olympiad in Physics, Chemistry, Biology,…, Chemistry, Unit III: Classification of Elements and Periodicity in Properties (read 29 Sept 2026).
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1.Among the following ions, which one has the LARGEST ionic radius?
- (A)O²⁻
- (B)F⁻
- (C)Na⁺
- (D)Mg²⁺
Show the answer and solution
Answer: (A) O²⁻
Solution: All are isoelectronic (10 electrons), but O²⁻ has the smallest nuclear charge (Z=8), resulting in the weakest attraction on the electron cloud and thus the largest ionic radius. The radius decreases: O²⁻ > F⁻ > Na⁺ > Mg²⁺.
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