Which equation expresses Boyle's law for an ideal gas with a fixed amount and constant temperature?

• A. p = constant
• B. pV = constant
• C. V = constant
• D. p/V = constant

Answer: (B)

For a fixed amount of gas at a constant temperature, the ideal gas law P V = n R T simplifies to P V = constant because n and T are constants. This means pressure and volume trade off so that their product stays the same: when volume decreases, pressure increases proportionally, and when volume increases, pressure decreases proportionally. This inverse relationship is Boyle’s law.

The other forms don’t match this behavior. Setting pressure as constant would imply volume can change without relation to pressure, which isn’t the inverse relation described by Boyle’s law. A constant volume would fix one variable, leaving no inverse trade-off between P and V. A constant ratio p/V would imply a direct proportionality between pressure and volume, which contradicts the inverse relationship that Boyle’s law states.