Here's why:

* Bromine (Br) is a halogen, found in Group 17 of the periodic table.

* Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net electrical charge.

* Bromine has 35 protons and 35 electrons in its neutral state.

* Bromide ion (Br⁻) is formed when bromine gains one electron, giving it 36 electrons and a net charge of -1.