Final answer:
Bromine (option D) is the element in period 4 with the highest electronegativity, following the trend that electronegativity increases toward the upper right corner of the periodic table.
Step-by-step explanation:
The element in period 4 with the highest electronegativity is option D, bromine. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons, and it generally increases from left to right across a period and from bottom to top within a group on the periodic table. Given that fluorine is the most electronegative element and cesium is the least electronegative, and recognizing that electronegativity increases diagonally from the lower left to the upper right, bromine being a non-metal close to fluorine on the table would be the most electronegative in the given options. Potassium, calcium, and copper have lower electronegativities as they are metals and are positioned more to the left in the periodic table.