Boiling point is defined as:

Boiling point is defined as:

• A. The temperature at which the vapour pressure equals atmospheric pressure
• B. The temperature at which a liquid boils at any pressure
• C. The temperature at which a liquid changes to a gas without boiling
• D. The temperature at which a solid becomes a liquid

Answer: (A)

Boiling point is about when a liquid’s vapor pressure becomes equal to the pressure surrounding it. At that temperature, bubbles of vapor form inside the liquid and rise to the surface, so the liquid boils. This is usually referenced at atmospheric pressure (about 1 atm), and the boiling point changes with pressure: higher external pressure raises it, lower pressure lowers it. Evaporation can happen below this temperature, but boiling requires the vapor pressure to match the surroundings, turning the liquid into vapor throughout. The other ideas mix up different processes: a liquid becoming a gas without boiling is evaporation, a solid turning into a liquid is melting.

Boiling point is about when a liquid’s vapor pressure becomes equal to the pressure surrounding it. At that temperature, bubbles of vapor form inside the liquid and rise to the surface, so the liquid boils. This is usually referenced at atmospheric pressure (about 1 atm), and the boiling point changes with pressure: higher external pressure raises it, lower pressure lowers it. Evaporation can happen below this temperature, but boiling requires the vapor pressure to match the surroundings, turning the liquid into vapor throughout. The other ideas mix up different processes: a liquid becoming a gas without boiling is evaporation, a solid turning into a liquid is melting.