Question
$A{l^{3 + }}$ has a lower ionic radius than $M{g^{2 + }}$ because
✓
Answer
b
$Al ^{3+}$ and $Mg ^{2+}$ have equal number of electrons and are, therefore, isoelectronic.
$Al ^{3+}$ and $Mg ^{2+}$ have equal number of electrons and are, therefore, isoelectronic.
For iso-electronic species, size depends upon the effective nuclear charge and size is inversely proportional to the effective nuclear charge. More is the positive charge, more is the effective nuclear charge and thus, lesser is the size.
Since the effective nuclear charge is greater in $Al ^{3+}$ than $Mg ^{2+}$, it has a smaller size than $Mg ^{2+}$.
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