Final answer:
A pie chart is the most useful type of chart for visually representing sets of data as parts of a whole, such as product categories within total sales.
Step-by-step explanation:
The most useful type of chart for visually representing sets of data as parts of a whole, such as product categories within total sales, is a pie chart.
In a pie chart, each category is represented by a wedge in a circle, and the size of each wedge corresponds to the percentage or proportion of the whole that category represents.
For example, if we have total sales of $100 and we want to show the sales of different product categories (Category A: $40, Category B: $30, Category C: $30), a pie chart would be most effective in showing the proportionate representation of each category within the total sales.