The element that is the most electronegative and reactive of all elements is Fluorine (F).

Here's why:

* Electronegativity: Fluorine has the highest electronegativity value on the Pauling scale (4.0). Electronegativity is a measure of an atom's ability to attract electrons towards itself when it forms a chemical bond. The higher the electronegativity, the stronger the attraction for electrons.

* Reactivity: Fluorine is extremely reactive due to its high electronegativity and small atomic size. Its outermost electron shell is only one electron short of being full, making it highly eager to gain an electron to achieve a stable octet configuration. It readily reacts with almost all other elements, often with explosive force.

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