Question

Which of the following statements is correct for boiling point of a liquid?

• A. Temperature at which a liquid boils at any pressure.
• B. Temperature at which solid is in equilibrium with its liquid.
• C. Temperature at which vapour pressure equals the applied pressure.
• D. Temperature at which applied pressure is greater than vapour pressure of liquid.

Hint:

This is why water boils at a lower temperature at high altitudes (like on a mountain). The applied atmospheric pressure is lower, so the liquid doesn't need to be heated as much for its vapour pressure to catch up and equal it.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to identify the precise thermodynamic definition of the boiling point of a liquid.

Step 2: Detailed Explanation:
As a liquid is heated, its molecules gain kinetic energy, causing more of them to escape into the gas phase. This process steadily increases the liquid's vapour pressure.
Boiling occurs only when the vapour pressure pushing outward from the liquid perfectly matches the external atmospheric (or applied) pressure pushing down on it.
Once these two pressures are equal, bubbles of vapour can form freely within the bulk of the liquid and rise to the surface.
Therefore, the boiling point is strictly defined as the temperature at which the vapour pressure of the liquid equals the external applied pressure.

Step 3: Final Answer:
The correct statement corresponds to option (C).