The term molarity (M) refers to how many moles there are for eve one liter. 0.2 M is (0.2 moles/L), which means 0.250 L is 0.05 moles (0.2/4) in terms of a 0.2 M solution. If you have 0.05 moles, and a 4 M solution (4 moles/L), then you would need to divide 1 liter by 80 (0.05 x 80 = 4). Hence, the answer to this question is 0.0125 liters.