Where do we find the most abundant natural supply of cl- ions

Chlorine is found abundantly in earth crust and ocean.

Explanation:

The elements of group 17 are called halogens. These are six elements Fluorine, Chlorine, Bromine, Iodine, Astatine. Chlorine is one of them.

it is greenish-yellow irritating gas.

its melting point is 172.2 K

its boiling point is 238.6 K

It is present in earth crust and ocean abundantly.

In ocean chlorine is found in the form of salt sodium chloride.

About 1.9% mass of sea water consist of chlorine ions.

In earth crust it is present in minerals such as carnallite and sylvite.

it is disinfectant and can kill the bacteria.

it is also used in manufacturing of paper, paints and textile industries.

It is also reported that chlorine can effect the respiratory system, immune system and heart.

Up to some extent it can also effect the organism living in water.