Chlorine occur in rock salt which is known as sodium chloride the other salts like magnesium chloride and calcium chloride are also exist. In Pakistan chlorine is found in the form of sodium chloride.

The laboratory chlorine gas is prepared by the oxidation of hydrochloric acid with manganese dioxide as a result chlorine gas and water is formed. on industrial scale, chlorine is prepared by electrolysis of concentrated sodium chloride which is known as brine solutions.

This process is carried out in a special type of cell called nelson cell. The physical properties of chlorine are that the color of chlorine gas is greenish yellow and there smell is unpleasant. They are not completely soluble in water. chlorine gas is heavier than air and can be easily liquefied.The chemical properties of chlorine gas are that when it react with sodium to form sodium chloride

.

Chlorine reacts with copper to copper chloride. When it reacts with potassium bromide to form potassium chloride and bromine is formed. Chlorine reacts with water to form hydro choleric acid and hypo choleric acid. Chlorine gas is used as a germicide. It is use as a bleaching agent.Chlorine is very useful for the preparation of different chemicals.