The molarity of a substance is the number of moles of the substance present per liter. We are given the mass per liter, which is 292 grams. We may convert this into moles by dividing by the molecular mass of magnesium nitrate. This is:
Mg + 2 * NO₃⁻
24 + 2 * (14 + 16*3)
Mr = 148 g/mol
The molarity of the solution is:
M = 292/148 = 1.97 moles / liter
The solution has a molarity of 1.97 M