Under what condition does the liquid start boiling?

Boiling is the process by which a liquid turns into vapor when it is heated to its boiling point. The transition from the liquid phase to the gaseous phase occurs when the vapor pressure of the liquid is equal to the atmospheric pressure exerted on the liquid. Boiling is a physical change and molecules are not chemically altered during this process. When the atoms or molecules of a liquid are able to expand enough to move from a liquid phase to a gaseous phase, bubbles form and boiling occurs.