Question

Which of the following is the correct order of ionic radii?

• A.
  $T{i}^{4+}<M{n}^{7+}$
• B. $C{a}^{2+}<K^{+}$
• C. $O^{2-}<F^{-}$
• D. $C{l}^{-}<K^{+}$

Answer 1

The correct option is B $C{a}^{2+}<K^{+}$

Ionic radius is the distance from the nucleus of an ion up to which it has an influence on its electron cloud.

Ions are formed when an atom loose or gain electrons. When an atom loose an electron it forms a cation and when it gains an electron it becomes an anion.

Increase in nuclear charge increases the effective nuclear charge and hence results in decrease in ionic radius. So (a) is incorrect.

$K^{+}$ and $C{a}^{2+}$ are isoelectronic species. The latter ion have higher effective nuclear charge so its radius will be less than $K^{+}$.
Size of $K^{+}$ is equal to the size of $C{l}^{-}$.
Effective nuclear charge of $F^{-}$ is greater than that of $O^{2-}$. Hence $O^{2-}$ is greater than $F^{-}$.