106. Solving a chemistry problem

822. For the bimolecular reaction of the persulfate ion with the bromide ion (-> products), the following dependence of the rate constant on the ionic strength at 25°C has been established.
I, mmol/dm^3 2.45 3.65 4.45 6.45 8.45 12.45
K, dm^3 * mol^-1 * c^-1 1.05 1.12 1.16 1.18 1.26 1.39
Determine the constant at zero ionic strength and the charge of the persulfate ion z, knowing the charge of the bromide ion - 1 (charge z should be rounded up to an integer).