If the pressure and temperature of a gas are held constant and some gas is added to the container or some is allowed to escape a change is can be observed?

If the pressure and temperature of a gas are held constant and gas is added or removed from the container, the volume of the gas will change according to Boyle's Law. Adding gas will increase the volume, while escaping gas will decrease it. This relationship is governed by the ideal gas law, where the volume is directly proportional to the number of moles of gas when pressure and temperature remain unchanged. Therefore, any change in the quantity of gas affects the volume of the gas in the container.