Why are alkaline-earth metals strong reducing agents?

Alkaline-earth metals are strong reducing agents because their atoms possess two valence electrons in an outermost s orbital that are relatively easily removed. The chemistry of these elements is defined by this ionization, as the atoms readily lose these two electrons to form stable, doubly charged $M^{2+}$ ions.12

By giving up these electrons to other substances, the metals facilitate the reduction of those substances, which is the defining characteristic of a reducing agent. While removing the second electron requires more energy than the first, this expenditure is compensated for by the significant binding energy gained when the metal forms stable ionic compounds or interacts with a solvent. As one moves down the periodic table from beryllium to barium, the ionization energy generally decreases, reflecting an increase in electropositive character and reactivity.21