Chlorine (Cl) is a chemical element with atomic number 17. There are two stable chlorine isotopes, ³⁵Cl and ³⁷Cl, of which ³⁵Cl is the more common.

Chlorine is part of many chemical compounds including common salt (NaCl) and hydrochloric acid (HCl) which is produced in our stomachs to help digest food the food we eat.