Question

The correct order of increasing ionic radius for $F^{-},N{a}^{+},S^{2-},C{l}^{-}$ and $K^{+}$ is:

• A. $F^{-}<N{a}^{+}<S^{2-}\approx C{l}^{-}<K^{+}$
• B. $N{a}^{+}<K^{+}<F^{-}<C{l}^{-}\approx S^{2-}$
• C. $N{a}^{+}<F^{-}\approx K^{+}<C{l}^{-}<S^{2-}$
• D. $N{a}^{+}\approx F^{-}<C{l}^{-}<S^{2-}<K^{+}$

Answer 1

The correct option is C $N{a}^{+}<F^{-}\approx K^{+}<C{l}^{-}<S^{2-}$

On moving down the group, ionic radius increases due to increase in principle quantum number. Hence, $N{a}^{+}<K^{+}$ and $F^{-}<C{l}^{-}$.
For isoelectronic species, size depends on the number of protons. The ion having the greater number of protons will have smaller size due to the increase in the effective nuclear charge. Thus $C{l}^{-}<S^{2-}$
However, $K^{+}$ and $F^{-}$ have similar size.
So, the order of ionic size follows the order: $N{a}^{+}<F^{-}\approx K^{+}<C{l}^{-}<S^{2-}$