Ionic and atomic radii trends for isoelectronic species

Steps:

• Examine electron configurations: Na⁺, Ne, F⁻ all have 10 electrons (isoelectronic).
• For isoelectronic species, radius increases as nuclear charge (protons) decreases, weakening electron attraction.
• Na⁺ has 11 protons (smallest), Ne has 10 (medium), F⁻ has 9 (largest).
• Verify other options lack this increasing trend.

Why D is correct:

• Na⁺, Ne, F⁻ are isoelectronic; per the trend, ionic radius increases with decreasing effective nuclear charge (Zeff = protons - shielding), from Na⁺ (Zeff highest) to F⁻ (Zeff lowest).

Why the others are wrong:

• A: Neutral atoms N > O > F in size (decreases across period 2 due to increasing Zeff).
• B: Mg²⁺ (12 protons, 10 electrons) < Na⁺, so Na⁺ to Mg²⁺ decreases in size.
• C: O²⁻ (8 protons, 10 electrons) > F⁻, so Na⁺ < O²⁻ > F⁻, not increasing.

Final answer: D