What is the boiling point of a liquid?

The boiling point of a liquid is defined as the temperature at which the vapor pressure of the liquid equals the external pressure surrounding the liquid. This phenomenon indicates that the liquid can transition into a gas, as the molecules have gained enough energy to overcome the intermolecular forces holding them in the liquid state.

At this temperature, bubbles of vapor can form within the liquid, which is a characteristic of boiling. The boiling point can vary depending on the external pressure; for example, at higher altitudes where the atmospheric pressure is lower, liquids will boil at lower temperatures than they would at sea level. Understanding this concept is essential for various applications in chemistry, cooking, and industrial processes.

The other options refer to different physical processes: ignition relates to combustion, freezing pertains to the transition from liquid to solid, and evaporation describes the process of molecules escaping from the liquid's surface at any temperature, not necessarily at the boiling point.