If you put the gas jar in the freezer, the gas pressure in the gas will decrease. This is because temperature and pressure of gases are directly related to each other. By putting the jar in the freezer, you are reducing the temperature, this will make the gas particles to lose kinetic energy and move slowly in the container, as their movement is now slow, they will collide less frequently with one another and with the wall of the container, thus decreasing the pressure.
