The most reactive group of metals is the alkali metals, which are found in Group 1 of the periodic table. These metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Here's why they are so reactive:

* One valence electron: They have only one electron in their outermost shell, which they readily lose to achieve a stable electron configuration.

* Low ionization energy: It takes very little energy to remove this single valence electron.

* Large atomic radius: Their large size means that the outermost electron is held less tightly by the nucleus.

This combination of factors makes alkali metals highly reactive with water, oxygen, and other substances. In fact, they react so violently with water that the heat generated can cause the hydrogen gas produced to ignite.