Question

The ions $O^{2-},F^{-},N{a}^{+},M{g}^{2+},andA{l}^{3+}$ are isoelectronic. Their ionic radii shows :

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

Answer 1

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

We know that an anion is larger than a neutral atom and a cation is smaller than a neutral atom. Greater the magnitude of charge on an anion, greater will be the size. Smaller the charge on the cation, greater will be the size.
Using the concepts mentioned above we have
$O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}>A{l}^{3+}$
Hence option D is the right answer.