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COMEDK2025ChemistryClassification of Elements and Periodicity in PropertiesActual

Arrange the following ions in the decreasing order of their ionic radii: Cl ⁻, Ca ²⁺, S ²⁻, K ⁺

Options

  1. ACl ⁻> S ²⁻> Ca ²⁺> K ⁺
  2. BCa ²⁺> K ⁺> Cl ⁻> S ²⁻
  3. CK ⁺> Ca ²⁺> S ²⁻> Cl ⁻
  4. DS ²⁻> Cl ⁻> K ⁺> Ca ²⁺

Correct answer

D. S ²⁻> Cl ⁻> K ⁺> Ca ²⁺

Step-by-step solution

The given ions are Cl ⁻ , Ca ²⁺ , S ²⁻ , and K ⁺ . First, determine the number of electrons in each ion: S ²⁻ has 16 + 2 = 18 electrons. Cl ⁻ has 17 + 1 = 18 electrons. K ⁺ has 19 - 1 = 18 electrons. Ca ²⁺ has 20 - 2 = 18 electrons. All these ions are isoelectronic, meaning they have the same number of electrons ( 18 ). For isoelectronic species, the ionic radius decreases as the nuclear charge (atomic number, Z ) increases, because a higher nuclear charge pulls the same number of electrons more strongly towards th

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