Why is the volume of a gas inversely proportional to pressure?

• A. P1 x V1 = P2 x V2...because as volume increases, there is less opportunity for particles to collide
• B. P1/T1 = P2/T2... temperature relation
• C. P1 + V1 = P2 + V2
• D. P1 - V1 = P2 - V2

Answer: (A)

Pressure in a gas comes from molecules colliding with the container walls. If you keep the temperature and the amount of gas fixed and you increase the volume, the gas has more space to move, so collisions with the walls become less frequent and, on average, less force is exerted per unit area. That means the pressure drops. This behavior is captured by Boyle’s law: the product of pressure and volume stays constant (P times V remains the same) when temperature and the amount of gas don’t change. So, as volume goes up, pressure goes down, showing the inverse relationship.

The other expressions involve temperature changes or different kinds of relationships, which don’t describe how pressure and volume relate at constant temperature and amount.