Electronegativity is the tendency for an atom to attract electrons. This tendency increases as you move upward and to the right on the periodic table. Of the given options, chlorine is the farthest up and to the right, so it is the most electronegative. The least electronegative atom would be selenium, as it is the lowest and leftmost option.

Electronegativity is a property that describes an atom's ability to attract and bond to electrons. There numerical estimates for the electronegativity of elements which differences can be used to estimate whether a bond is ionic, nonpolar covalent, or covalent. Within each period of the periodic table, there is an increase in electronegativity from left to right. Electronegativity also decreases with increasing atomic number in each group with minor exceptions among transition metals.