The most reactive element is fluorine. It is never found in its free form in nature. Because it has seven electrons in its outer energy level, fluorine is always on the lookout to find a single electron to give it a more stable configuration.
At first, scientists had a hard time isolating fluorine, according to Jefferson Lab. The element fluorine belongs to the group of elements called the halogens. In general, the halogens are the most reactive nonmetals on the periodic table.
For nonmetals, the trend of reactivity increases as you go up a group of elements. According to this trend, fluorine then would be the most reactive element in the group of halogens.