Question

The ions $O^{2-},F^{-},N{a}^{+},M{g}^{2+}$ and $A{l}^{3+}$ are isoelecronic. Their ionic radii show :

• A. An increase from $O^{2-}$ to $F^{-}$ and then decrease from $N{a}^{+}$ to $A{l}^{3+}$
• B. An decrease from $O^{2-}$ to $F^{-}$ and then increase from $N{a}^{+}$ to $A{l}^{3+}$
• C. A significant increase from $O^{2-}$ to $A{l}^{3+}$
• D. A significant decrease from $O^{2-}$ to $A{l}^{3+}$

Answer 1

Answer: (D)

On increasing atomic number of isoelectronic species ionic radii decreases due to increasing effective nuclear charge
$(Z_{eff})$ Radius $\propto \frac{1}{Z_{eff}}$
So, as the negative charge increases ionic radii increases while on increasing positive charge ionic radii decreases. Anions having higher ionic radii than the cation. $O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}>A{l}^{3+}$