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The correct order of the decreasing ionic radii among the following  isoelectronic species are:


  • Option 1)

    Ca2+ > K+ > S2- > Cl-

  • Option 2)

    Cl > S2- > Ca2+ > K+

  • Option 3)

    S2- > Cl > K+ > Ca2+  

  • Option 4)

    K+ > Ca2+  > Cl- > S2-


Answers (1)

First, we note that this is an isoelectronic series of ions, with all ions having 18 electrons. In such a series, size decreases as the nuclear charge (atomic number) of the ion increases. The atomic numbers of the ions are S (16), Cl (17), K (19), and Ca (20). Thus, the ions decrease in size in the order S2–> Cl–> K+> Ca2+.

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Amit Kumar

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