The halogens are five non-metallic elements found in group 17 of the periodic table. The term "halogen" means "salt-former" and compounds containing halogens are called "salts". All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1.
If you drop a bath bomb into water, then it will fizz because a chemical reaction is taking place.
Unequal heating of the atmosphere
The density does not change because it is still the same liquid as before
