To determine the correct chemical formula for magnesium bromide, we need to consider the valencies of the constituent elements, magnesium (Mg) and bromine (Br), and how they combine to form a neutral compound.
1. Determine the valencies:
- Magnesium (Mg) typically has a valency of +2. This means a magnesium ion has a charge of [tex]\( +2 \)[/tex] (notated as [tex]\( Mg^{2+} \)[/tex]).
- Bromine (Br), as an ion, is called bromide and typically has a valency of -1. This means a bromide ion has a charge of [tex]\( -1 \)[/tex] (notated as [tex]\( Br^{-} \)[/tex]).
2. Neutralizing the charges:
- To form a neutral compound, the total positive charge must equal the total negative charge.
- One magnesium ion ([tex]\( Mg^{2+} \)[/tex]) with a charge of +2 will need two bromide ions ([tex]\( Br^{-} \)[/tex]), each with a charge of -1, to balance the charges.
3. Forming the chemical formula:
- Since it takes two bromide ions to balance the charge of one magnesium ion, the chemical formula must reflect this 1:2 ratio.
- Therefore, the correct chemical formula for magnesium bromide is [tex]\( MgBr_2 \)[/tex].
Thus, the correct answer is:
A. [tex]\( MgBr_2 \)[/tex]
