Why didn't scientists know about atoms for a long time

It has been two weeks since charles met with daniel, a dietitian, who provided charles with a menu for weight loss. charles and his mother are going back to see daniel again with a chart of the food charles has eaten. the following lists what charles ate in one day: breakfast 1 banana, 1 cup of nonfat milk, 1 egg lunch 1 cup of carrots, 3 oz of steak, 1 apple, 1 cup of nonfat milk dinner 6 oz of skinless chicken, 1 baked potato, 3 oz of broccoli, 1 cup of nonfat milk

Aballoon inflated with three breaths of air has a volume of 1.7 l. at the same temperature and pressure, what is the volume of the balloon if five more same-sized breaths are added to the balloon?

Iknow #2 is d. i just need to know why