Here's why:

* Electron Configuration: Bromine's electron configuration is [Ar] 3d¹⁰ 4s² 4p⁵.

* Valence Electrons: Valence electrons are the electrons in the outermost energy level of an atom. In bromine's case, the outermost energy level is the 4th energy level, which contains the 4s² and 4p⁵ electrons.

* Total Valence Electrons: 2 (from the 4s subshell) + 5 (from the 4p subshell) = 7 valence electrons.