Final answer:
A pie graph would be the best visual aid to show the percentage of each state's population between the ages of 18 and 25 in 2010.
Step-by-step explanation:
If you are writing a report on the population of the United States and want to show the percentage of each state's population between the ages of 18 and 25 in 2010, the most appropriate visual aid would be a pie graph. A pie graph allows you to divide the population into different categories (in this case, age groups) and show the relative sizes of each category as a percentage of the whole. By using a pie graph, you can visually compare the proportion of 18-25 year-olds in each state.