Final answer:
The statement is true; bar graphs use vertical bars of varying heights to visually compare the values they represent, such as size or quantity.
Step-by-step explanation:
The statement "A blank chart compares differences in values by showing vertical sizes relative to the values they represent" is true. Bar graphs are visual representations used to compare the size, quantity, rates, distances, and other quantitative categories. The bars in a bar graph can represent different entities such as countries or years, and the vertical axis typically shows the numerical or percentage values associated with these entities. The height of each bar corresponds to the value it represents. Therefore, by comparing the heights of the bars in a bar graph, one can easily see the differences in values.