When the temperature of a gas is decreased, its volume decreases. This is because the gas molecules slow down, causing less collisions with the walls of the container and therefore less pressure.

Here's why:

* Kinetic Molecular Theory: The Kinetic Molecular Theory states that gas molecules are in constant random motion, and their average kinetic energy is directly proportional to the absolute temperature.

* Decreased Temperature, Decreased Kinetic Energy: When temperature decreases, the average kinetic energy of the gas molecules decreases. This means they move slower.

* Less Collisions: Slower molecules collide less frequently with the walls of the container.

* Reduced Pressure: Reduced collisions mean less pressure exerted on the container walls.

* Volume Contraction: To maintain a constant pressure, the volume of the gas must decrease to compensate for the reduced number of collisions.

This relationship between temperature and volume is summarized by Charles's Law:

V₁/T₁ = V₂/T₂

Where:

* V₁ is the initial volume

* T₁ is the initial temperature

* V₂ is the final volume

* T₂ is the final temperature

Important Note: This relationship holds true only if the pressure and amount of gas remain constant.