Question

Identify the correct order of the size of the following.

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

Answer 1

The correct option is B

$C{a}^{2+}<K^{+}<Ar<C{l}^{-}<S^{2-}$

A cation has always the lesser ionic size than „ metal atom due to loss of electrons and an anion always the greater size than metal atom due to of electrons. The given species are isoelectronic species as they contain same number of electrons. For isoelectronic species ionic radii is
$\propto \frac{1}{atomicnumber}$.
Ions $C{a}^{2+},K^{+},Ar,S^{2-},C{l}^{-}$ have their atomic number as 20, 19,18,16,17 respectively.
So, the correct order of size is as
$C{a}^{2+}<K^{+}<Ar<C{l}^{-}<S^{2-}$