Final answer:
A Run Chart is used to monitor a process variable over time, identifying trends and cycles, whereas Pie Charts show parts of a whole and Pareto Charts display categories sorted by size.
Step-by-step explanation:
The graphical tool used to monitor a process variable over time and is helpful in identifying trends and cycles is the Run Chart. Unlike a Pie Chart, which shows parts of a whole, or a Pareto Chart, which displays categories sorted by size, the Run Chart uses a line to track changes in data over time. This tool is particularly useful for spotting trends and variations in a process, making it easy to see increases, decreases, or patterns that occur.