What type of graph is used to illustrate the relationship between two quantitative variables?

The scatter plot is the appropriate choice for illustrating the relationship between two quantitative variables. This type of graph displays individual data points on a two-dimensional axis, where each axis represents one of the quantitative variables. By plotting the data in this way, a scatter plot allows for the visualization of patterns, correlations, and trends that may exist between the two variables.

For instance, if you were to analyze how a person's height correlates with their weight, each individual's height would be plotted on one axis and their weight on the other. The resulting cluster of points can help identify whether there is a positive, negative, or no correlation between height and weight.

In contrast, a bar graph is typically used for categorical data to compare different groups or categories. A line graph is best suited for showing trends over time, as it connects data points sequentially to indicate changes over intervals. A histogram portrays the distribution of a single quantitative variable by grouping data into bins, thereby not focusing on the relationship between two variables.