The halogens are present in combined form as they are highly reactive. The main source of fluorine is fluorspar or fluorite. The other ores of fluorine are cryolite, fluroapatite. The main source of chlorine is sodium chloride from sea water. Bromides and iodides also occur in sea water.
The common physical properties of the group 17 elements are listed in the table.
Chlorine is highly reactive hence it doesn’t occur free in nature. It is usually distributed as various metal chlorides. The most important chloride is sodium chloride which occurs in sea water.