Which statement describes Boyle's Law?

• A. At constant temperature, the absolute pressure and the volume of gas are inversely proportional.
• B. As temperature increases, gas volume increases linearly.
• C. Gas density is independent of pressure at fixed temperature.
• D. Pressure equals density times velocity squared.

Answer: (A)

For a fixed amount of gas at a constant temperature, pressure and volume are inversely related. This means the product of pressure and volume stays the same: P × V is constant. If you compress the gas to half its volume, the pressure roughly doubles because molecules collide with the container walls more often when space is reduced.

This holds only when the amount of gas is unchanged and the temperature remains constant. If temperature changes, the relationship changes and you’d use other gas laws.

Other statements don’t fit because one describes temperature driving volume directly (Charles’ Law), which is a different relationship. Another claims density is independent of pressure at fixed temperature, which isn’t true—density actually increases with pressure at the same temperature. The last option uses a dynamic pressure form from fluid dynamics (pressure related to density and velocity), which isn’t the gas-law relationship described here.