Final answer:
According to Boyle's law, if the number of particles and temperature are constant and pressure increases, the volume of the gas decreases.
Step-by-step explanation:
When the number of particles and temperature of a gas is held constant, and the pressure increases, the volume of the gas decreases. This behavior is explained by Boyle's law, which states that for a given amount of gas at a constant temperature, the volume of a gas is inversely proportional to its pressure. This means that as pressure goes up, volume must come down when temperature is steady.