What law states that when pressure is held constant, the volume of a gas is directly proportional to its temperature in Kelvins?

The law that states when pressure is held constant, the volume of a gas is directly proportional to its temperature in Kelvins is Charles' Law. This relationship can be represented mathematically by the equation V/T = k, where V is the volume, T is the temperature in Kelvins, and k is a constant value for a given amount of gas at a fixed pressure.

Charles' Law illustrates that as the temperature of a gas increases, its volume also increases, provided the pressure remains unchanged. This can be understood by considering that increasing the temperature causes the gas particles to move more vigorously, leading to an expansion in volume.

While Boyle's Law deals with the relationship between pressure and volume at constant temperature, Avogadro's Law pertains to the relationship between the volume of a gas and the number of moles of gas at constant temperature and pressure. The Ideal Gas Law combines several gas laws, including Boyle's and Charles', but it does not solely focus on the relationship described in the question. Therefore, the correct identification of Charles' Law clearly fits the scenario where pressure is constant and volume is directly proportional to temperature in Kelvins.