Frost on a propane bottle is what kind if reaction

I think it is a physical reaction since it is water freezing due to the expansion of the liquid propane to propane gas that takes the energy from the surroundings which happens two include water vapor.

It would be an endothermic reaction, as it is absorbing heat and causing the surrounds to get colder.

You would be correct, boiling water does disinfect contamination.    the property of disinfecting means to kill  germs, bacteria and other pathogens or contamination  that might cause an infection or cause a person to become sickly. a couple methods of disinfecting are using soap, other cleaning supplies or by simply "boiling" the contaminate.  the reason why boiling water disinfects certain attributes is because some cells cannot survive the heat and pressure.