A gas at 65°C occupies 4.22 L. At what Celsius temperature will the volume be 3.87 L, assuming that pressure remains constant?

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)

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.

Solubility would be your answer.