Question

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

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

Answer 1

Answer: (B)

a significant decrease from $O^{2-}$ to $A{l}^{3+}$

As all the given species are iso electronic, the ionic radii decreases with increasing atomic number as effective nuclear charge increases. Hence from $O^{2-}$ to ${Al}^{3+}$, the size decreases significantly i.e., option B.