In a 0.1 M solution of sodium chloride NaCl , the concentration of chloride ions Cl- will also be 0.1 M. This is because sodium chloride dissociates completely in water, forming one sodium ion Na+ and one chloride ion Cl- for each molecule of NaCl. Therefore, the concentration of Cl- ions will be equal to the concentration of the NaCl solution.Using a chloride ion-selective electrode, you would measure the concentration of chloride ions directly, and the result should be approximately 0.1 M, assuming the solution is well-mixed and the electrode is functioning properly.