What is the most chemically active element?

Fluorine is the most chemically reactive element on the periodic table, and there are no chemical substances that are capable of freeing it from its bonds. The most reactive metallic element is francium, which is radioactive and has no stable isotopes. Cesium is the most reactive metal with stable isotopes.

Fluorine causes an explosive reaction when mixed with hydrogen. When a stream of pure fluorine gas is directed at a concrete block, the fluorine also causes the concrete to spontaneously ignite. Fluorine is so reactive that it cannot naturally occur in nature, and it was incredibly difficult for scientists to isolate it in its pure form.