Which term describes the temperature at which a liquid begins to boil?

• A. Initial Boiling Point and Boiling Range
• B. Melting Point
• C. Auto-ignition Temperature
• D. Vapor Pressure

Answer: (A)

Boiling begins when the liquid’s vapor pressure equals the surrounding pressure, and the onset temperature where that first bubbling starts is called the initial boiling point. Some liquids don’t have a single sharp boiling point and instead boil over a range of temperatures, which is described as the boiling range. In safety and chemical data contexts you’ll often see the paired term “initial boiling point and boiling range” to capture both aspects of when a liquid starts to boil. The other terms refer to different properties: melting point is solid to liquid, auto-ignition temperature is the point at which a substance will ignite without a flame, and vapor pressure is the pressure exerted by vapor in equilibrium with the liquid at a given temperature.