The most active of all the chemical elements is a halogen known as fluorine (F).

Here's why:

* Electronegativity: Fluorine has the highest electronegativity of all elements. This means it has a strong pull on electrons, making it highly reactive.

* Reactivity: Fluorine readily forms bonds with other elements, often with explosive results. It's so reactive that it can even react with noble gases like xenon.

* Oxidation Potential: Fluorine has a very high oxidation potential, meaning it readily gains electrons, further contributing to its reactivity.

While chlorine, bromine, and iodine are also halogens, their reactivity decreases as you move down the periodic table.