Which statement correctly describes Boyle's Law?

• A. Decreasing pressure causes volume to increase at constant temperature.
• B. Increasing temperature causes volume to increase at constant pressure.
• C. Increasing amount of gas under constant P and V increases pressure.
• D. Increasing pressure increases volume.

Answer: (A)

Boyle's law shows an inverse relationship between pressure and volume for a fixed amount of gas at constant temperature: the product P times V stays the same. So when pressure decreases while temperature is held steady, the volume must increase to keep PV constant. That’s why the statement describing decreasing pressure causing volume to increase at constant temperature is correct.

The other ideas mix in different gas relationships: increasing temperature at constant pressure is Charles’s law, not Boyle’s. Increasing the amount of gas at fixed P and V would raise pressure (PV = nRT shows P is proportional to n when V and T are fixed). And increasing pressure while keeping volume the same would not happen under Boyle’s law—it would imply a violation of the inverse P–V relationship.