As the density of air decreases, its pressure

As the density of air decreases, its pressure

• A. Increases
• B. Remains constant
• C. Decreases
• D. Fluctuates

Answer: (C)

When a gas has lower density, there are fewer molecules in a given volume to collide with the container walls. Pressure arises from these collisions, so fewer collisions mean lower pressure. For a gas like air, and at constant temperature, pressure is proportional to density (P = ρRT/M). That means as density decreases, pressure decreases. This matches everyday observations, like higher up where air is thinner and the pressure is lower. The idea that pressure would stay constant or vary unpredictably doesn’t fit the direct link between how many molecules are present and how hard they push on the walls. Therefore, pressure decreases.

When a gas has lower density, there are fewer molecules in a given volume to collide with the container walls. Pressure arises from these collisions, so fewer collisions mean lower pressure. For a gas like air, and at constant temperature, pressure is proportional to density (P = ρRT/M). That means as density decreases, pressure decreases. This matches everyday observations, like higher up where air is thinner and the pressure is lower. The idea that pressure would stay constant or vary unpredictably doesn’t fit the direct link between how many molecules are present and how hard they push on the walls. Therefore, pressure decreases.