In the polarographic method, the concentration of a substance can be determined by comparing the measured current with the limiting current. The limiting current is the maximum current that can be achieved when the concentration of the substance is at its highest. The ratio of the measured current to the limiting current can be used to determine the concentration of the substance in the sample.First, we need to find the ratio of the measured current to the limiting current:Ratio = Measured current / Limiting current Ratio = 3.5 mA / 5.2 mA Ratio = 0.6731Now, we need to know the concentration of the substance when the limiting current is reached. This information is usually provided in the form of a calibration curve or a standard curve, which relates the concentration of the substance to the limiting current. Without this information, we cannot determine the exact concentration of the substance in the sample.However, if you have the calibration curve or standard curve, you can use the ratio calculated above to find the concentration of the substance in the sample by multiplying the ratio by the concentration at the limiting current.