When air in a syringe is compressed such that there is no change in temperature, the

Analyze the question: Air in a syringe is compressed (the volume is reduced) while the temperature stays constant. We need to say what happens.

Concept: Boyle's Law At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume:

P₁V₁ = P₂V₂

Step-by-step solution:

1. Pushing the plunger reduces the volume of the air (V decreases).
2. Temperature is constant, so Boyle's Law applies: if V decreases, P must increase.
3. Check each option: • A. Air liquefies: Wrong. Liquefying a gas needs very low temperature and very high pressure. Simple compression at room temperature in a syringe will not do this. • B. Pressure increases: Correct. Smaller volume means the molecules hit the walls more often, so the pressure rises. • C. Intermolecular space increases: Wrong. Compression pushes the molecules closer together, so the space between them decreases. • D. Density decreases: Wrong. The same mass is squeezed into a smaller volume, so density (mass/volume) increases.

Answer: B. Pressure increases

Exam tip: For any "compression at constant temperature" question, remember: Volume ↓, Pressure ↑, Density ↑, Spacing ↓. Boyle's Law is about pressure and volume moving in opposite directions.