Which law states that at constant temperature the pressure of a given amount of gas is inversely proportional to the volume of the gas?

Boyle's law

Justification:

1) Robert Boyle (1627 - 1691) was a chemist born in Ireland who made an experiment to study the relationship between the pressure and the volume of a gas.

2) He proved that if the temperature remains constant, when the pressure is doubled, the volumen reduces to half. And when the pressure is reduced to half the volumen is doubled.

3) The inverse relation, where one variable increases when the other is reduced, is mathematically  expressed as:

PV = constant, or P₁V₁ = P₂V₂.

Then, Boyle's law states that the volume of a certain amount of gas at constant temperature varies inversely with the pressure.

Google it that might work