Question

Which is the correct order of ionic size?

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

Answer 1

The correct option is D $C{a}^{+2}<K^{+}<Ar<C{l}^{-}<S^{2-}$

Atomic radii decrease across a period. Cations are smaller than their parent atoms. Among isoelectronic species, the one with the greater positive nuclear charge will have a smaller radius.
Hence the order will be:
$C{a}^{+2}<K^{+}<Ar<C{l}^{-}<S^{2-}$