Fluorine
no, chlorine is not metallic, but it can come in various forms, most commonly a yellowish gas.
Fluorine is the most chemically reactive non-metallic element. (Fluorine is the most reactive of all the elements, actually.) It is known as the hungry wolf of the periodic table - and it earned that nickname.
Fluorine is the most reactive element.
Fluorine(F2) is the most reactive element, known to react with even Xenon, Krypton, Gold, Platinum, etc.
Group 17, the halogens
Oxygen (O) is a chemical element with the atomic number 8. It is a highly reactive nonmetal that is essential for life and plays a key role in various biological and geological processes. Oxygen is the most abundant element in the Earth's crust and atmosphere.
If by vital you mean most reactive, then the metal francium, Fr, is the most reactive element.
Fluorine
Potassium is most reactive with the element Oxygen. However, it should be noted that it is most reactive with a non-element: Water.
The most reactive is fluorine.
Oxygen.
The most non-metallic element is fluorine. It is a highly reactive, corrosive gas and belongs to the halogen group in the periodic table. Fluorine has a strong tendency to gain electrons and form negative ions in chemical reactions.