Under what conditions does Charles' Law apply?

Charles' Law applies under conditions of constant pressure. This law states that the volume of a gas is directly proportional to its temperature when measured in Kelvin, provided the pressure remains unchanged. This relationship is critical in understanding how gases behave when they are heated or cooled, allowing for predictions about volume changes in response to temperature fluctuations without introducing new factors like pressure variations.

The essence of Charles' Law is rooted in the ideal behavior of gases, where at constant pressure, increasing the temperature will result in an increase in volume and vice versa. This principle is fundamental in various applications, such as in hot air balloons, where heating the air inside causes the balloon to rise due to increased volume at a constant pressure.

While the other options suggest different conditions that may affect gas behavior, they do not align with the principle established by Charles' Law, which specifically requires that pressure remain constant to observe the direct relationship between temperature and volume.