Final answer:
Cesium has the lowest electronegativity among the given elements with an electronegativity value of 0.79, which makes it the least electronegative nonradioactive element on the periodic table.
Step-by-step explanation:
The element with the lowest electronegativity among the given options of Cesium, Strontium, Calcium, and Barium is Cesium. According to Pauling's electronegativity values, electronegativity increases diagonally from the lower left to the upper right of the periodic table. Therefore, since Cesium is situated in the lower left of the periodic table, it has the lowest electronegativity value, which is 0.79. This makes Cesium the least electronegative nonradioactive element on the periodic table.