Given the average concentration of silver is 28 ppb = 28 x0.001
mg/LÂ Â Â Â Â Â Â Â Â Â Â Â
Since 1 ppb = 0.001 mg/L
                                                                       Â
= 0.028 mg/L
                                                                       Â
= 0.028x10-3 g/L
Molar mass of silver is 107.9 g/mol
So number of moles of silver ion is = mass/molar mass
                                                 Â
= (0.028x10-3 g) / (107.9 g/mol)
                                                 Â
= 2.59x10-7 mol
So Molarity of silver ion , M = Number of moles / Volume of
solution in L
                                      Â
= 2.59x10-7 mol / 1L
                                      Â
= 2.59x10-7 M