Another important source of chloride ions is from sea water.
Chloride ions are also needed to prevent a buildup of positive charge.
If you have a water-softener, that usually adds chloride ion to the water.
If chloride ions have penetrated beyond the surface more rigorous treatment is required.
These reactions are catalyzed by the presence of chloride ions.
Your tongue can tell the difference between a chloride ion and a chlorine molecule.
It contains carbon in its +4 oxidation state and chloride ions.
I'm pretty sure they would have a "package" for measuring chloride ion in the ppm range.
In the form of chloride ions, chlorine is necessary to all known species of life.
Since a chloride ion is a good leaving group, it will be readily replaced with the nucleophile.