How does decreased pressure affect gas?

When the pressure on gas decreases, the gas particles have more space to move around, allowing them to expand. This behavior can be explained by the physical laws governing gases, particularly Boyle's Law, which states that for a given amount of gas at constant temperature, the pressure and volume are inversely related. As pressure decreases, the volume increases, leading to an expansion of the gas.

In contrast, actions like gas contraction would generally occur under increased pressure, while concepts such as gas toxicity or dissolving pertain to specific chemical properties or interactions rather than the basic physical behavior of gases in response to pressure changes. Thus, the correct choice reflects the fundamental principle that gases will expand when the pressure surrounding them is reduced.