Here's why:
* Vapor Pressure: The pressure exerted by the vapor of a liquid in equilibrium with its liquid phase.
* External Pressure: The pressure of the surrounding environment.
* Boiling Point: The temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid.
When the vapor pressure of a liquid equals the external pressure (1 ATM in this case), the liquid can overcome the atmospheric pressure and change into a gas, forming bubbles within the liquid. This is the process of boiling.
