Which statement correctly defines the boiling point of a substance?

Which statement correctly defines the boiling point of a substance?

• A. Temperature of a substance when the vapor pressure equals atmospheric pressure.
• B. Temperature at which a solid becomes a liquid.
• C. Minimum temperature at which a liquid gives off enough vapors to form an ignitable mixture with air near the surface of the liquid.
• D. Temperature at which vapors form an inhalation hazard independent of pressure.

Answer: (A)

Boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding pressure. When this balance occurs, bubbles of vapor form inside the liquid and rise to the surface, signaling that the liquid is boiling and turning into vapor. This point depends on pressure: higher surrounding pressure raises the boiling point, while lower pressure lowers it. The other statements describe melting (solid to liquid), flammable vapor formation related to ignition (a flammability concept, not the boiling definition), or inhalation hazard considerations that don’t define when a liquid boils. So the definition that matches boiling point is the one where vapor pressure equals the ambient pressure.

Boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding pressure. When this balance occurs, bubbles of vapor form inside the liquid and rise to the surface, signaling that the liquid is boiling and turning into vapor. This point depends on pressure: higher surrounding pressure raises the boiling point, while lower pressure lowers it. The other statements describe melting (solid to liquid), flammable vapor formation related to ignition (a flammability concept, not the boiling definition), or inhalation hazard considerations that don’t define when a liquid boils. So the definition that matches boiling point is the one where vapor pressure equals the ambient pressure.