What accounts for the high reactivity of alkali metals?

Alkali metals, found in Group 1 of the periodic table, possess a single valence electron in their outermost electron shell. This characteristic significantly influences their reactivity. The presence of just one electron means that these elements are highly eager to lose that electron in order to achieve a stable electron configuration, akin to that of noble gases. When an alkali metal loses its valence electron, it forms a positively charged ion (cation), which contributes to their high reactivity.

The energy required to remove that single valence electron is relatively low when compared to other elements with multiple valence electrons. This ease of losing the outermost electron explains why alkali metals react vigorously, especially with nonmetals.

In contrast, other choices hint at different characteristics. Options discussing multiple valence electrons or gaining electrons do not accurately describe alkali metals, as their reactivity is specifically due to the loss of that one electron rather than gaining multiple. Likewise, noble gases, known for their lack of reactivity due to having full valence electron shells, do not represent the behavior of alkali metals. Hence, the understanding of reactivity in alkali metals is fundamentally grounded in their single valence electron, making them very reactive when they lose it