Boiling maintains constant temperature during phase change

Steps:

• Recall that boiling is a bulk liquid process at boiling point where vapor forms throughout.
• Note evaporation is surface-only, occurring at any temperature below boiling point.
• Evaluate each statement against these definitions.
• Identify the true statement about temperature constancy in boiling.

Why D is correct:

• During boiling, the temperature remains constant at the boiling point as added heat provides latent heat of vaporization, per the phase change principle.

Why the others are wrong:

• A: Boiling occurs throughout the liquid, not just at the surface.
• B: Evaporation happens at any temperature, not only high ones.
• C: Evaporation cools the liquid by absorbing latent heat from it.

Final answer: D