The temperature at which a substance changes from a liquid to a gas is called its boiling point.

However, it's important to note that:

* Boiling point is dependent on pressure. The higher the pressure, the higher the boiling point. This is why water boils at a lower temperature at higher altitudes.

* There is also a concept of "vapor pressure" which is the pressure exerted by the vapor of a liquid at a given temperature. When the vapor pressure equals the surrounding atmospheric pressure, the liquid boils.

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