Question

Arrange the following in the increasing order of ionic size.
$N^{3-},N{a}^{+},F^{-},O^{2-},M{g}^{2+}$

• A. $M{g}^{2+}<N{a}^{+}<F^{-}<O^{2-}<N^{3-}$
• B. $N^{3-}<N{a}^{+}<F^{-}<O^{2-}<M{g}^{2+}$
• C. $M{g}^{2+}>N{a}^{+}>F^{-}>O^{2-}>N^{3-}$
• D. $N{a}^{+}<M{g}^{2+}<F^{-}<N^{3-}<O^{2-}$

Answer 1

The correct option is A $M{g}^{2+}<N{a}^{+}<F^{-}<O^{2-}<N^{3-}$

Ionic size increases with the addition of electrons and ionic size decreases with the loss of electrons. The nitride ion, has 10 electrons in contrast to only 7 protons. It has high inter electronic repulsions due to which it has the maximum size. The increasing order of ionic size is $M{g}^{2+}<N{a}^{+}<F^{-}<O^{2-}<N^{3-}$.

They are isoelectronic species with same number of electrons. Higher is the atomic number, higher will be the effective nuclear charge, lower will be the size.