Under constant amount and temperature, if volume is reduced, pressure increases.

• A. Remains the same
• B. Decreases
• C. Cannot be determined
• D. Increases

Answer: (D)

This tests Boyle's Law: for a fixed amount of gas at a constant temperature, pressure and volume move in opposite directions. The relationship P V = n R T shows that when n and T are constant, pressure is proportional to nR T divided by volume, so P = (nR T)/V. If you reduce the volume, the same amount of gas at the same temperature must exert more pressure to fit into the smaller space. For example, halving the volume doubles the pressure, assuming ideal behavior. The other options would violate this inverse relationship under these conditions, since lowering volume cannot leave pressure unchanged or reduce it when n and T stay the same.