If a gas at constant temperature is compressed to half its original volume, what happens to the pressure?

• A. Halves
• B. Remains the same
• C. Doubles
• D. Quadruples

Answer: (C)

Gas pressure and volume are inversely related when the temperature and amount of gas stay the same. This follows Boyle’s law: PV = constant. If you compress the gas so the volume becomes half, the pressure must double to keep the product PV constant. Intuitively, with less space for the same number of molecules, they hit the container walls more often, raising pressure while the temperature remains unchanged. So the pressure doubles. The other options don’t fit because halving the pressure would violate PV = constant, keeping pressure the same would require no volume change, and quadrupling would happen only if the volume dropped to a quarter, not half.