Q: Why alkali metals are more reactive than alkaline earth metals?
Alkali metals are highly reactive metals. Their reactivity is generally higher than the alkaline earth metals. The electronic configuration of alkali metals is ns1, and that for the alkaline earth metals is ns2. Therefore, just by releasing one electron from their outermost shell, they can attain stable (inert gas-like) electron configuration, whereas the alkaline earth metals need to remove two electrons for the same goal. So, their ionization energies are lower and oxidation potentials are higher than corresponding alkaline earth metals (barring a few exceptions, of course). Moreover, for similar reasons alkali metals engage only one electron per atom towards their metallic bonding framework, making them softer metals compared to the alkaline earth metals, and consequently, their heats of atomization is considerably lower. All these factors contribute towards making alkali metals more reactive than alkaline earth metals. Their reactivity increases again, on descending down the group.