Which element has the least electronegative value?

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The trend in electronegativity on the periodic table shows that electronegativity generally decreases as you move down a group and increases as you move across a period from left to right.

Francium, being located at the bottom of Group 1 (alkali metals), has the lowest electronegativity of all the elements. This is due to its larger atomic size and the increased distance between the nucleus and the valence electron, which weakens the nucleus's ability to attract electrons from other atoms.

In contrast, helium, being a noble gas, possesses a complete electron shell and does not form bonds that involve electron sharing, but its electronegativity is considered higher compared to francium. Sodium and potassium, located higher in the periodic table within the same group, also have higher electronegativities than francium, though they, too, are less electronegative than elements in higher periods and groups.

Therefore, francium is the element with the least electronegative value among the choices provided.