Question:
The ionic radii of $\mathrm{K}^{+}, \mathrm{Na}^{+}, \mathrm{Al}^{3+}$ and $\mathrm{Mg}^{2+}$ are in the order:
Correct Option: , 3
Solution:
$\mathrm{Al}^{3+}, \mathrm{Mg}^{2+}$ and $\mathrm{Na}^{+}$are isoelectronic ionic species.
For monoatomic ionic isoelectronic species as positive charge increases ionic size decreases.
The order of size of $\mathrm{Na}^{+} \& \mathrm{~K}^{+}$is $\mathrm{Na}^{+}<\mathrm{K}^{+}$,
$\therefore$ order of ionic radii is : $\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{K}^{+}$