What happens to water when it reaches 100°C and starts to boil?

• A. It freezes into ice
• B. It remains at 100°C while boiling
• C. Temperature increases above 100°C immediately
• D. It condenses back into water

Answer: (B)

When water reaches 100°C at standard atmospheric pressure, it undergoes a phase change from liquid to gas, also known as boiling. During this boiling process, the temperature of the water remains constant at 100°C. This constant temperature is due to the energy supplied for the phase change being used to convert the liquid phase into the gas phase rather than increasing the temperature. Even though heat continues to be applied, the additional energy is absorbed in the form of latent heat, which is necessary for the molecules to overcome the intermolecular forces that hold them in the liquid state.

Thus, the key aspect of this process is that the boiling temperature is maintained until all the water has turned to steam, ensuring that the temperature does not rise above 100°C during this phase change at atmospheric pressure.