In a closed circuit, if the volume decreases, what happens to the pressure of a gas?

In a closed circuit, according to Boyle's Law, when the volume of a gas decreases, the pressure of that gas increases, provided the temperature remains constant. Boyle's Law states that for a given mass of an ideal gas at constant temperature, the pressure of the gas is inversely proportional to its volume. This means that if the volume reduces, the molecules of the gas have less space to move around, leading to more frequent collisions with the walls of the container, which results in an increase in pressure.

Therefore, the correct answer is that the pressure increases when the volume decreases in a closed circuit.