Which of the following statements about volatile liquids is correct? They have

Step 1: Analyze the question We need to identify the properties of volatile liquids, specifically their vapour pressure and boiling point.

Step 2: The concept A volatile liquid is one that evaporates easily at room temperature. This happens when the forces between its molecules (intermolecular forces) are weak.

• Weak intermolecular forces mean molecules escape into the gas phase easily, so the vapour pressure is high.
• A liquid boils when its vapour pressure equals the external (atmospheric) pressure. If the vapour pressure is already high at a low temperature, it reaches atmospheric pressure quickly, so the boiling point is low.

Step 3: Apply to the options

• A. High vapour pressure and low boiling point: correct, as explained above.
• B. High vapour pressure and high boiling point: contradictory, because high vapour pressure leads to a low boiling point.
• C. Low vapour pressure and low boiling point: contradictory, because a low boiling point needs a high vapour pressure.
• D. Low vapour pressure and high boiling point: this describes a non-volatile liquid, such as glycerol or oil.

Step 4: Answer The correct option is A.

Examples: Ethanol, ether, and petrol are volatile liquids. They evaporate quickly, which is why you smell petrol so easily at a filling station.

Exam tip: Remember that volatile = vaporises easily = high vapour pressure = low boiling point. Vapour pressure and boiling point always move in opposite directions when you compare liquids. If you see an option where both are high or both are low, you can eliminate it.