The most reactive non-metal is fluorine, and it is also the most reactive element that scientists have discovered. Fluorine combines readily with almost any substance, including metals that are usually stable.
Fluorine gas was first isolated in 1886 through a complicated electrolysis procedure. Due to its high reactivity, it is also difficult to store. It reacts with water, metals and even glass containers which it is kept in. Despite the fact that fluorine is toxic in large doses, trace amounts of the element are added to water supplies to prevent tooth decay.