Question

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

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

The correct option is D A significant decrease from $O^{2-}$ to $A{l}^{3+}$

All the four ions are isoelectronic but the ionic radii differs because each ion possesses different nuclear charges.

The cation with a greater positive charge will have a smaller radius owing to the increase in the effective nuclear charge.

The anion with a greater negative charge will have a larger radius owing to the repulsion between the electrons.

Thus, the order of decreasing ionic radii is:
$O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}>A{l}^{3+}$