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For isoelectronic species, size of anion increases as negative charge increases whereas size of cation decreases with increase in positive charge. Further ionic radii of anions is more than that of cations. Thus the correct order is Ca²⁺ < K⁺ < Ar < Cl⁻ < S²⁻.

1. Ca²⁺ < K⁺ < Ar < Cl⁻ < S²⁻
2. Due to odd number of electrons in ClO₂⁻, it is expected to exhibit paramagnetic behaviour.
3. None of the above.
4. None of the above.

Correct answer: Ca²⁺ < K⁺ < Ar < Cl⁻ < S²⁻

Solution

The given order of ionic radii is correct because for isoelectronic species, the size decreases with increasing nuclear charge (more protons pull electrons closer). Anions are larger than cations due to electron repulsion in negatively charged species.

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