Which of the following cannot be used as standard solution for determination of cell constant of conductivity cell?

Step-by-step solution

Saturated KCl Solution : A saturated solution of KCl is not typically used as a standard solution for conductivity calibration. The reason is that a saturated KCl solution may have variable composition due to temperature changes, partial crystallization, and difficulty in ensuring a uniform, reproducible concentration. Thus, it does not have a precisely known or easily reproducible conductivity value as the other standard concentrations do. Conclusion : Out of the given options, the saturated KCl solution (Option D