Molarity or molar concentration is a measure of the concentration of a chemical species, of a solute in a solution, using as units, number of moles, and volume in liters. The formula for Molarity is:
M = n/V
Where:
n = number of moles
V = volume in Liters
But we need the number of moles, and we will find it using the given mass, 27.5 grams and the molar mass of MgBr2, 118.113g/mol
118.113g = 1 mol
27.5g = x moles
x = 0.233 moles of MgBr2
Now we can use the molarity formula:
M = 0.233/0.125
M = 1.86
The molarity is 1.86 M