Answer
The molar concentration of $Br^-$ ions in this solution is equal to 0.675 $M$.
Work Step by Step
As we can identify by its chemical formula, each $FeBr_3$ has 3 $Br^-$ ions.
$\frac{0.225 mol(FeBr_3)}{1 L} \times \frac{3 mol(Br^-)}{1 mol (FeBr_3)} = 0.675M(Br^-)$
