An increase in the pressure exerted on gas at a constant temperature results in

Correct answer: a decrease in volume (Boyle’s law).

Explanation: At constant temperature (and fixed amount of gas), pressure and volume are inversely related: \(P \propto \tfrac{1}{V}\). So, increasing the external pressure compresses the gas, reducing its volume.

• a decrease in the number of effective collisions – Incorrect. Compression increases concentration; collision frequency tends to increase, not decrease (temperature is unchanged).
• a decrease in volume – Correct.
• an increase in the average intermolecular distance – Incorrect. Compression brings particles closer, so the average distance decreases.
• an increase in volume – Incorrect. Opposite of Boyle’s law.