Latent heat of vaporization during boiling

Steps:

• At 100°C, added thermal energy is latent heat, keeping temperature constant.
• This energy overcomes intermolecular attractions, increasing molecular separation from liquid to gas phase (3).
• Intermolecular forces remain the same strength but act over larger distances, so they do not decrease (1 incorrect).
• Molecules in steam gain translational freedom, increasing their average speed despite constant temperature (2).

Why C is correct:

• Latent heat increases potential energy (separation, 3) and enables higher molecular speeds in the gas phase (2), per kinetic molecular theory at constant temperature.

Why the others are wrong:

• A includes 1, but forces do not decrease—energy separates molecules against existing forces.
• B includes 1 and excludes 3, but forces unchanged and separation must increase for vaporization.
• D excludes 2, but gas molecules exhibit increased speed due to phase transition.

Final answer: C