Which chart helps to monitor the proportion of defects in samples?

An R-chart, or range chart, is used to monitor the variability within a process by tracking the range of values in a sample. It focuses on the dispersion of measurements rather than the proportion of defects. Therefore, it does not provide insights into defect rates, making it unsuitable for this purpose.

A C-chart, or count chart, is utilized for tracking the number of defects in a fixed sample size. While it can monitor defects, it does not express the proportion of defects relative to the total number of items inspected, which is crucial for understanding defect rates. Thus, it is not the appropriate choice for monitoring proportions.

S-charts, or standard deviation charts, are employed to monitor the variability of a process based on standard deviation calculations. Like the R-chart, it tracks variance rather than the proportion of defective items. Therefore, it does not serve the purpose of monitoring defect proportions.