Which graphical representation is used to illustrate the relationship between two variables for a group of individuals?

A scatterplot is the appropriate graphical representation to illustrate the relationship between two variables for a group of individuals. This visual tool displays individual data points on a Cartesian plane, with one variable represented along the x-axis and the other along the y-axis. By plotting these points, a scatterplot allows for easy identification of trends, correlations, or patterns between the two variables.

For example, if you were analyzing the relationship between hours studied and exam scores, each student's hours studied and their corresponding score could be plotted on the scatterplot. Observing the distribution of points could help in understanding whether there is a positive correlation (as hours studied increase, scores also tend to increase), a negative correlation, or no correlation at all.

In contrast, a histogram represents the distribution of a single variable and is useful for displaying frequency data. A bar chart is designed to compare different categories and is not suited for showing relationships between two continuous variables. A line graph typically illustrates trends over time and is not the best choice for showing relationships between different variables without a time component. Thus, the scatterplot stands out as the most effective method for visualizing the relationship between two variables in a dataset.