On the periodic table, electronegativity generally increases as you move from left to right across a period and decreases as you move down a group. As a result, the most electronegative elements are found on the top right of the periodic table, while the least electronegative elements are found on the bottom left.
Element Electronegativity
P 2.1
C 2.5
Br 3.0
At 2.2
Hence, the correct order is Br > C > At > P.