23.8 g/mol Since the definition of molar mass is mass per mole, just divide the mass of the sample by the number of moles you have. So 0.250 g / 1.05x10^-2 mol = 23.8095 g/mol Since our input data only has 3 significant figures, you need to round the result to 3 significant figures. 23.8095 g/mol rounds to 23.8 g/mol