Which of the following tools helps us to understand the spread and shape of a distribution of a process data?

The histogram is the tool that effectively helps to understand the spread and shape of a distribution of process data. It provides a visual representation of the frequency distribution of a set of continuous data points, allowing you to see how often each range of values occurs. The bars of the histogram correspond to the intervals (or bins) of data, and the height of each bar indicates the number of occurrences within that interval. This format allows for the easy identification of the central tendency, dispersion, and the overall shape of the distribution, such as whether it is normal, skewed, or has other characteristics.

In contrast, while a box plot does summarize a data set and indicates variability with quartiles and outliers, it does not provide as detailed an understanding of the distribution shape compared to a histogram. Control charts are primarily used to monitor process stability over time in a quality control framework, focusing on identifying trends and variations rather than the shape of the data distribution. Scatter diagrams are used to understand relationships between two variables, which is different from analyzing the distribution of a single dataset. Thus, the histogram distinctly stands out as the appropriate tool for understanding the spread and shape of a distribution in this context.