Here's why:

* Atomic Number: Bromine (Br) has an atomic number of 35, meaning it has 35 protons and 35 electrons.

* Electron Configuration: The electron configuration of bromine is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵.

* Shells: The numbers in front of the orbitals (1, 2, 3, 4) represent the electron shells.

Therefore, bromine has four electron shells (n=1, n=2, n=3, and n=4).