Na2so4 is dissolved in water to make 450 ml of a 0.250 m solution. what is the molar mass of na2so4, and how many moles are needed?

Molarity is Given as,

                       Molarity  =  Moles / Volume of Solution  --- (1)

Data Given:
                   Molarity  =  0.250 mol.L⁻¹

                   Volume  =  450 mL  =  0.45 L

Solving equation 1 for Moles,

                    Moles  =  Molarity × Volume

Putting values,

                    Moles  =  0.250 mol.L⁻¹ × 0.45 L

                    Moles  =  0.1125 mol

Now, converting moles into grams,
As,
                    Moles  =  Mass / M.mass
Or,
                    Mass  =  Moles × M.mass

                    Mass  =  0.1125 mol × 142 g.mol⁻¹

                    Mass  =  15.97 g

Result:
            Molar Mass of Na₂SO₄  =  142 g.mol⁻¹

            Moles needed  =  0.1125 mol

The correct answer is "atomic weight".