Answer:
Least electronegative is radon, Ra
Step-by-step explanation:
The higher the electronegativity, the more that element will attract electrons. Fluorine is the most electronegative. It only needs one more electron to fill its outer shell. Plus, it is a smaller element than many, so the positive charge on the nucleus plays a key role in the attraction.
Elements on the lower left of the periodic table have the lower electronegativities. In fact, they will happily surrender an electron so that the outer electron shell appears more like that of a noble gas. Of this list, Radon is the least electronegative. It would prefer giving up, not gain, electrons.
Electronegativities
Ra 0.9
Be 1.57
Mg 1.31
Sr 0.95
Ca 1.00
Radon, Ra, is the least electronegative.