You mix 15g of sugar in enough water to make 1 L of solution The concentration of this solution is?

15 grams sugar per liter is the concentration, in terms of mass per volume. To express the concentration in molarity (assuming the sugar is sucrose):

15 g sucrose * (1 mole sucrose / 342 g sucrose) / 1 L = 0.0439 M aqueous sucrose