Question

Identify the correct order of the size of the following.

• A. $Ca^{2+} < K^+ < Ar < S^{2-} < Cl^{-}$
• B. $Ca^{2+} < K^+ < Ar < Cl^- < S^{2-}$
• C. $Ar < Ca^{2+} < K^+ < Cl^- < S^{2-}$
• D. $Ca^{2+} < Ar < K^+ < Cl^- < S^{2-}$

Answer 1

The Correct Option is B

The question requires us to arrange the given ions and atom in order of increasing size. To solve this, we need to understand the concept of ionic and atomic radii:

1. Atomic and Ionic Radii: Atomic radii increase down a group in the periodic table and decrease across a period from left to right. Generally, anions (negatively charged ions) are larger than their parent atoms because of the additional electron(s) which increase electron-electron repulsion within the shell.
2. Ionic Size Comparison:
   • Ca^{2+}: A cation formed by losing two electrons, making it smaller than the neutral atom due to reduced electron-electron repulsion.
   • K^+: A cation formed by losing one electron. It is larger than Ca^{2+} but smaller than a neutral Ar atom.
   • Ar: A noble gas atom with no charge, it is larger than K^+.
   • Cl^-: An anion formed by gaining one electron, larger than Ar due to increased electron-electron repulsion.
   • S^{2-}: An anion formed by gaining two electrons, even larger than Cl⁻ due to more electron repulsions.
3. Order of Size: Based on this understanding, the order of size from smallest to largest is:
   • Ca^{2+} <
   • K^+ <
   • Ar <
   • Cl^− <
   • S^{2-}

Therefore, the correct order based on the options given is Ca^{2+} < K^+ < Ar < Cl^- < S^{2-}. This option correctly represents the increasing order of size from the smallest to the largest species.