“Importance” is a relative term, so for something to be important, it needs to be important for a particular process. Generally, most people are interested in whether something is important for human life. In the case of chlorine it certainly is important for living things and human civilization. The first thing people usually think about with chlorine is how people “add chlorine” to pools. Chlorine isn’t added as a single element, but rather as a compound with sodium and oxygen that is often referred to as bleach.

Chlorine kills bacteria and other microscopic things in the water that could make people sick. However, if too much chlorine is added to the water, it would be dangerous to humans too because chlorine is very reactive. Chlorine is also important for humans, mostly because it’s paired with sodium in the form of table salt, sodium chloride. Because of this, your body has ways to deal with chlorine since most sodium atoms come with chlorine atoms.

Chlorine is an element and one of the more common elements. It is in particular the primary anion in sea salt, with the result that life has adapted to use it because it is so common. Chlorine is necessary to all known species of life in the form of chloride ions

Chlorine is an important chemical in water purification and in disinfectants; it is an essential micro nutrient for higher plants where it concentrates in the chloroplasts.