Classification of Elements Part 2

Concept:Atomic/ionic radii trends are based on periodic position and effective nuclear charge; electron gain enthalpy (magnitude) follows periodic trends across groups and periods.Explanation:Statement I:The order given is $Al > Mg > Mg^{2+} > Al^{3+}$.$Mg$ and $Al$ are in the same period (3).Across a period, atomic radius decreases due to increasing effective nuclear charge.Thus, $Mg > Al$ in radius, not $Al > Mg$.$Mg^{2+}$ and $Al^{3+}$ are isoelectronic (both have 10 electrons, like $Ne$).For isoelectronic species, higher nuclear charge gives smaller radius.$Al^{3+}$ has $Z = 13$, $Mg^{2+}$ has $Z = 12$, so $Al^{3+} < Mg^{2+}$.The correct order is $Mg > Al > Mg^{2+} > Al^{3+}$.Therefore, Statement I is false.Statement II:Electron gain enthalpy magnitude becomes more negative across a period and less negative down a group for nonmetals.Among halogens: $Cl$ has the most negative EGE, followed by $Br$.$O$ and $S$ are in group 16; $S$ has more negative EGE than $O$ due to less electron repulsion in a larger orbital.Thus, the order $Cl > Br > S > O$ is correct for magnitude (more negative first).Therefore, Statement II is true.Answer:Option C: Statement I is false but Statement II is true.