In a 0.1 M solution of potassium chloride KCl , the concentration of potassium ions K+ is equal to the concentration of the KCl solution, since KCl dissociates completely into K+ and Cl- ions in solution. Therefore, the concentration of potassium ions in a 0.1 M KCl solution is 0.1 M. Using a potassium ion-selective electrode, you would calibrate the electrode with a series of standard potassium solutions of known concentrations. Then, you would measure the potential voltage of the 0.1 M KCl solution and compare it to the calibration curve to confirm the concentration of potassium ions in the solution. In this case, the electrode should indicate a concentration of 0.1 M K+.