Alkali metals have the lowest electronegativity values among all elements. This is because they have only one valence electron, which is loosely held and easily lost.

Here's why:

* Electronegativity measures an atom's ability to attract electrons in a bond.

* Alkali metals are in Group 1 of the periodic table. They have one electron in their outermost shell.

* Low ionization energy: Alkali metals easily lose their valence electron, making them highly reactive.

* Large atomic radius: As you move down the group, the atomic radius increases, making the valence electron further from the nucleus and easier to remove.

Therefore, Francium (Fr) has the lowest electronegativity among all alkali metals.

Remember that electronegativity decreases as you move down a group in the periodic table.