Question

Statement - I: $M{g}^{2+}andA{l}^{3+}$ are isoelectronic but ionic radius $A{l}^{3+}$ is less than that of $M{g}^{2+}$.
Statement - II: The effective nuclear charge on the outer-shell electrons in $A{l}^{3+}$ is more than that in $M{g}^{2+}$

• A. Statement - I is true; Statement - II is true; Statement - II is correct explanation for Statement - I.
• B. Statement - I is true; Statement - II is true; Statement - II is NOT the correct explanation for Statement - I
• C. Statement - I is true; Statement - II is false
• D. Statement - I is false; Statement - II is true

Answer 1

The correct option is A

Statement - I is true; Statement - II is true; Statement - II is correct explanation for Statement - I.

$Mg$ has the configuration: $\left[Ne\right]3s^2$ and the cation has the same configuration as $Ne$. Likewise, $Al$ has a configuration of $\left[Ne\right]3s^{2}3p^1$. Hence, $A{l}^{3+}$ will also have the same configuration as the dipositive cation $M{g}^{2+}$. Hence they are isoelectronic for sure!

Aluminium has a surplus proton than magnesium. Hence, the $Z_{eff}$ of $A{l}^{3+}$ is higher and thus the ionic radius will be smaller than $M{g}^{2+}$. Statement I is correct and Statement II is also correct; the latter correctly explains the former!