What chemical property is characteristic of alkali metals?

Alkali metals are known for their high reactivity, particularly with water. When alkali metals, such as lithium, sodium, or potassium, come into contact with water, they react vigorously to form hydroxides and release hydrogen gas. This reactivity increases down the group; for example, cesium reacts more explosively with water than lithium. The resulting hydroxides produced are strongly alkaline, giving the alkali metals their name.

This characteristic reactivity is due to their electron configuration. Alkali metals have a single electron in their outermost shell, which they readily lose to achieve a stable electron arrangement, similar to that of the noble gases. This tendency to lose that one electron makes them very reactive, especially with substances like water that can accept it readily.

In contrast, other choices do not accurately reflect the behavior of alkali metals, as they are not stable in air and tend to tarnish quickly, nor do they have low reactivity with water. They also do not demonstrate stability at high temperatures, as they can undergo reactions or even spontaneous combustion under certain conditions.