Final answer:
A graph displaying the direct proportionality between the volume of a gas and its temperature under constant pressure demonstrates Charles's Law.
Step-by-step explanation:
A graph that shows that the volume of a gas is directly proportional to its temperature under constant pressure demonstrates Charles's Law. This law can be stated mathematically as V = const. T, where V is the volume of the gas and T is the temperature measured in Kelvins (K). According to Charles's Law, if the pressure is constant, as the temperature increases, the volume increases as well.