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The correct choice is the c-chart, which is specifically designed for counting defects when the focus is on the number of defects per unit of output. In quality control, c-charts are used in situations where the data consists of countable defects occurring in a fixed sample size or unit, making it ideal for monitoring the consistency of defect rates in a production process.

Using c-charts allows organizations to evaluate whether their processes are stable over time with respect to the number of defects generated. This tool is particularly valuable in identifying variations in quality that could lead to increased costs or customer dissatisfaction as it focuses directly on the number of defects observed in each unit.

Other statistical process control charts, while useful in their respective contexts, do not specifically address the count of defects per unit. For example, an R-chart monitors the variability of a process based on a measuring attribute, while a p-chart tracks the proportion of defective items in a sample. An individual chart focuses on individual measurements and is less effective when counting multiple defects within each unit.