Given the level of sulfate ion is 46.0 ppm

                                                = 46.0 mg / L

Molar mass of sulfate ion , SO₄^2- is = At.mass of S + (4xAt.mass of O )

                                                         = 32 + (4x16)

                                                         = 96 g/mol

So the concentration of sulfate ion is = [SO₄^2- ] = 46.0 mg / L

                                                                           = 46.0x10^-3 g / L   Since 1g = 10³ mg

                                                                           = 46.0x10^-3 gx(1/96)(mol/g) /L

                                                                           = 4.79x10^-4 mol/L

                                                                           = 4.79x10^-4 M