To identify the correct chemical formula for magnesium bromide, we need to consider the valency or charge of the ions involved.
1. Magnesium (Mg) is an alkaline earth metal and belongs to Group 2 of the periodic table. Consequently, it has a valency of 2, meaning it forms ions with a charge of +2 ([tex]\( \text{Mg}^{2+} \)[/tex]).
2. Bromine (Br) is a halogen and belongs to Group 17 of the periodic table. It has a valency of 1, meaning it forms ions with a charge of -1 ([tex]\( \text{Br}^- \)[/tex]).
To neutralize the charges, one magnesium ion ([tex]\( \text{Mg}^{2+} \)[/tex]) will pair with two bromide ions ([tex]\( \text{Br}^- \)[/tex]). This results in the formula:
[tex]\[
\text{Mg}^{2+} + 2 \cdot \text{Br}^- \Rightarrow \text{MgBr}_2
\][/tex]
So, the chemical formula of magnesium bromide is [tex]\( \text{MgBr}_2 \)[/tex].
Therefore, the correct answer is:
A. [tex]\( \text{MgBr}_2 \)[/tex]
