Q.Compare the alkali metals and alkaline earth metals with respect to

1. Ionisation enthalpy Alkaline earth metals (ns$^2$) have a smaller atomic radius and higher effective nuclear charge than the alkali metal of the same period (ns$^1$), so their first ionisation enthalpy (IE$_1$) is higher than that of the corresponding alkali metal. Their second ionisation enthalpy (IE$_2$) is only modestly higher than IE$_1$ (removing the second ns electron still gives a stable noble-gas core), whereas an alkali metal's IE$_2$ is enormously higher than its IE$_1$ (that electron must come from a filled, stable core).
2. Basicity of oxides For the same period, the alkali metal oxide (M$_2$O) is more ionic/basic than the alkaline earth metal oxide (MO), because the alkali metal ion has a lower charge and larger size (lower charge density/polarising power) than the alkaline earth ion, giving a more purely ionic, more strongly basic oxide.
3. Solubility of hydroxides …

Compare same-period pairs (e.g. Na vs Mg): higher nuclear charge/smaller size gives Group 2 the higher IE$_1$; the lower charge and larger size of Group 1 cations makes their oxides more …

• Comparing elements from different periods instead of matching each alkali metal with the alkaline earth metal of the same period.
• Assuming higher ionisation enthalpy of Group 2 also means their oxides are more basic — basicity actually goes the other way (Group 1 oxides are more bas …