Scientists after many experiments explain how the temperature of a gas

You first develop a hypothesis which is a guess or a prediction to explain a certain phenomenon.
Then, the hypothesis is tested to develop a theory. A theory replaces the hypothesis after doing tests that confirm the hypothesis.

Based on this:
Scientists after many experiments managed to explain how the temperature of the gas depends on the energy of its molecules.
THIS SENTENCE IS DESCRIBES A THEORY.

Ithink this is what you meant. the temperature at which a liquid begins to boil is called the boiling point. the boiling point of water is 212°f or 100°c.  and at that point will start to turn into steam (gas)