Boiling occurs when the vapour pressure of a liquid is
Answer Details
Boiling occurs when the vapor pressure of a liquid becomes equal to the atmospheric pressure. When the vapor pressure of a liquid reaches atmospheric pressure, it means that the pressure of the vaporized liquid is enough to overcome the atmospheric pressure, and the liquid starts to boil. This means that the liquid is converting into gas, and bubbles of gas are forming in the liquid and rising to the surface.
Think of it this way: when you heat up a pot of water, the heat causes the water to vaporize, or turn into steam. As the steam rises, it creates pressure, and if that pressure is strong enough to overcome the atmospheric pressure, the steam will escape from the pot and you'll see boiling.