Question

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

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

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

As we move along a period, size decreases, and as we move down the group size increases so here

	Z	electron
$N{a}^{+}$	11	10
$M{g}^{2+}$	12	10
$A{l}^{+3}$	13	10
$F^{-}$	9	10

$O^{2-}$ 8 10
Above are isoelectronic species, hence size $\propto \frac{1}{Z}$
So size decreases from $O^{-2}$ to $A{l}^{+3}$.

Option $D$ is correct.