The process of changing from a liquid to a gas is called vaporization, and it requires heat.

Here's why:

* Molecules in a liquid: Liquid molecules are close together and have some attraction to each other.

* Adding heat: When you add heat, you give the molecules more energy. This energy causes the molecules to move faster and farther apart.

* Overcoming attraction: Eventually, the molecules have enough energy to overcome the attraction holding them together in the liquid state and escape into the air as a gas.

Examples:

* Water boiling on the stove

* Dry ice (solid carbon dioxide) turning into a gas at room temperature

* Perfume evaporating from a bottle

So, the answer to your question is hot.