Final answer:
When the temperature of a gas in an expandable container is increased while keeping the pressure constant, the volume of the gas will increase.
Step-by-step explanation:
When the temperature of a gas in an expandable container is increased while keeping the pressure constant, the volume of the gas will increase. This is due to the fact that an increase in temperature causes the gas molecules to move faster and collide with the container walls more frequently, resulting in an expansion of the gas and an increase in its volume. This relationship between temperature and volume of a gas at constant pressure is known as Charles's Law.