Which of the following lanthanoid ions is diamagnetic (second instance question — verifying Yb)? [Which of the following orders of ionic radii is correctly represented?]

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NEET Chemistry QUESTION #7412

Question 1

\(\text{H}^- > \text{H}^+ > \text{H}\)
\(\text{Na}^+ < \text{F}^- < \text{O}^{2-}\)✔️
\(\text{F}^- > \text{O}^{2-} > \text{Na}^+\)
\(\text{Al}^{3+} > \text{Mg}^{2+} > \text{N}^{3-}\)

Correct Answer Explanation

Ionic radii comparison:
Na⁺, F⁻, O²⁻ are isoelectronic (10 electrons). Increasing radius means decreasing nuclear charge:

Na⁺: Z=11 → smallest
F⁻: Z=9
O²⁻: Z=8 → largest

So: Na⁺ < F⁻ < O²⁻ ✓

Option (1) is wrong: H has 1 proton; H⁻ is larger (more electron repulsion) and H⁺ has no electron at all (just a proton, ~10⁻¹⁵ m). Option (4) is wrong as N³⁻ >> Al³⁺ in size.

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