Which formula expresses Boyle's Law?

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This question tests how pressure and volume relate for a gas when temperature and the amount of gas remain unchanged. The core idea is that the product of pressure and volume stays constant for a fixed amount of gas at a constant temperature. So, P1V1 = P2V2 expresses that inverse relationship: if you squeeze the gas to a smaller volume, the pressure increases proportionally, and if you expand the volume, the pressure drops, with temperature held steady. This is the precise way to relate the two states before and after a change in volume.

The other forms don’t capture that inverse, constant-product relationship. Writing P/V as the same on both states would imply a different, non-physical constraint. Adding pressure and volume together isn’t how these variables trade off. The equation P = nRT / V is the ideal gas law, which does describe pressure for a given temperature and amount of gas, but it’s a broader relation that doesn’t express the specific state-to-state constant-product condition Boyle’s law uses. In the scenario Boyle’s law describes, those conditions reduce the general law to P1V1 = P2V2.