Which one of the following statements is correct?

Both boiling and evaporation are surface phenomena.

Boiling is a surface phenomenon, but evaporation is a bulk phenomenon.

Both boiling and evaporation are bulk phenomena.

Boiling is a bulk phenomenon, but evaporation is a surface phenomenon.

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC NDA-2 – 2019

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The correct option is D) Boiling is a bulk phenomenon, but evaporation is a surface phenomenon.

Evaporation is the process where molecules at the surface of a liquid gain enough kinetic energy to overcome the intermolecular forces and escape into the gaseous phase. This occurs at any temperature below the boiling point and only happens at the liquid’s surface.
Boiling is the process where a liquid turns into a vapor when its vapor pressure equals the surrounding atmospheric pressure. This occurs at a specific temperature (the boiling point) and involves the formation of vapor bubbles *throughout* the volume (bulk) of the liquid, which then rise to the surface. It is a phenomenon that occurs throughout the bulk of the liquid, not just at the surface.

Think of boiling water: bubbles form at the bottom and rise. Think of a puddle drying up: the surface reduces as water evaporates. Sublimation is another phase transition, from solid directly to gas, and it is typically a surface phenomenon. Melting is a bulk phenomenon.

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