The vapor pressure of acetone is 100 mm Hg at 8 ºC, 400 mm Hg at 40 ºC, and 760 mm Hg at 56 ºC. What is the normal boiling point of acetone?

The normal boiling point of acetone is ##56^@ Celsius##.
The boiling point of a liquid is the temperature at which it goes from liquid to gas. This means that at that particular temperature, the liquid’s becomes equal to the pressure of its environment.
From this point on, the liquid’s temperature can no longer rise. At boiling point, all the heat provided to the liquid will be used to change its state from liquid to vapor.
GIven the fact the normal pressure is ##1 atm##, or ##760 mmHg##, acetone’s boiling point will be the temperature at which its vapor pressure reaches this value. Therefore, its boiling point is ##56^@ Celsius##.
One can see now how a liquid’s boiling point can vary to match a higher or lower .