If the volume of a gas is kept constant, what varies directly with temperature?

When the volume of a gas is held constant, the relationship that varies directly with temperature is the pressure of the gas, according to Gay-Lussac's Law. This law states that the pressure of a gas is directly proportional to its absolute temperature (measured in Kelvin) if the volume is constant.

As the temperature increases, the kinetic energy of the gas molecules also increases. This results in more frequent and forceful collisions with the walls of the container, leading to an increase in pressure. Conversely, if the temperature decreases, the kinetic energy diminishes, resulting in a decrease in pressure.

The other options do not directly relate to the behavior of gas under the specified conditions. In this scenario, volume is held constant, which invalidates the relevance of volume as a variable. Additionally, while mixing typically pertains to the combination of different gases, it does not describe a direct relationship between temperature and pressure in a single gas scenario. Therefore, the only correct choice that aligns with the principles of gas behavior is the pressure.