* Group Charges: Magnesium (Mg) is in Group 2, so it has a +2 charge. Bromine (Br) is in Group 17, so it typically has a -1 charge.

* Balancing Charges: For the compound to be neutral, the charges must balance. Since magnesium has a +2 charge, two bromide ions (each with a -1 charge) are needed to make the compound neutral.

Therefore, the oxidation state of Br in MgBr₂ is -1.