Shown below is a gas sample contained in a cylinder with a movable piston.

The temperature is decreased from 400 K to 200 K at constant pressure. Which of the following images illustrate the gas sample after?

Derive the relationship between pressure and volume of gas at a constant temperature using Charles's law and Gay-Lussac's law.

Consider the image below representing gas in a container that has no fixed volume. 

Draw a similar image representing the same gas at the same temperature except that the pressure is decreased by 2 atm.