Express the concentration of a 0.0390 M aqueous solution of fluoride, F-, in mass percentage and in parts per million. Assume the density of the solution is 1.00 g/mL.

In getting the concentration of the substance that has an aqueous solution of a fluoride of 0.039M, the density doesn't matter anymore you just have to multiply its solution to its molar mass that would came up to 0.7409g and then do the conversion that could lead to a 0.07409% (m/m). I hope you are satisfied with my answer and feel free to ask for more