Gallons contain halogens, which are highly reactive with oxygen

Halon is a general term for any of the several compounds that are composed of carbon, possibly hydrogen and halogens.

Generally, halogens are quite reactive while halons are found to be quite inert.

Halons that reach the upper atmosphere can break down under the ultraviolet light, releasing halogen radicals, for which 'highly reactive' will be  too mild a term. However, they do not really react much with diatomic oxygen.

idk what the options are but

these is a strong electrostatic attraction between the ions hence a lot of energy is needed to overcome this attraction

this is why the boiling points are so high

rising temperatures because when water vapor in the air is cooled, it condenses. it turns back into a liquid and attaches to dust particles in the air. these very small water droplets group together to form clouds