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Question: Answered & Verified by Expert
The ions $\mathrm{S}^{2-}, \mathrm{Cl}^{-}, \mathrm{K}^{+}, \mathrm{Ca}^{2+}$ are isoelectronic. Their ionic radii show
ChemistryStructure of AtomAP EAMCETAP EAMCET 2021 (23 Aug Shift 1)
Options:
  • A a decrease from $\mathrm{S}^{2-}$ to $\mathrm{Cl}^{-}$and then increase from $\mathrm{K}^{+}$to $\mathrm{Ca}^{2+}$
  • B an increase from $\mathrm{S}^{2-}$ to $\mathrm{Cl}^{-}$and then decrease from $\mathrm{K}^{+}$to $\mathrm{Ca}^{2+}$
  • C a significant decrease from $\mathrm{S}^{2-}$ to $\mathrm{Ca}^{2+}$
  • D a significant increase from $\mathrm{S}^{2-}$ to $\mathrm{Ca}^{2+}$
Solution:
1610 Upvotes Verified Answer
The correct answer is: a significant decrease from $\mathrm{S}^{2-}$ to $\mathrm{Ca}^{2+}$
For isoelectronic species, the ionic radii decrease with increase in nuclear charge.
So, the cation with greater + ve charge i.e. $\mathrm{Ca}^{2+}$ will have smaller radius and the anion with greater - ve charge i.e. $\mathrm{S}^{2-}$ will have a larger radius.
$\because$ The ionic radii show a significant decrease from $\mathrm{S}^{2-}$ to $\mathrm{Ca}^{2+}$.

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