Final answer:
The correct answer to the question is that the pressure decreases, which is option B.
Step-by-step explanation:
The behavior of an ideal gas in a closed system—like a cylinder with a movable piston—can be explained by the relationship between pressure, volume, and temperature known as Boyle's Law and Charles's Law.
For an ideal gas at constant temperature (isothermal conditions), Boyle's Law states that the pressure of the gas is inversely proportional to its volume. This means that if the volume of the gas increases, the pressure decreases, as there is more space for the gas particles to move around and therefore, they hit the walls of the container less frequently.
When the temperature is kept constant, as in the given scenario, and the volume of the cylinder is increased by moving the piston, the pressure exerted by the gas will decrease. This is because the gas molecules will have a greater area to move in and will collide with the walls of the cylinder less often, thus exerting less force on the walls.