Chlorine

Chlorine, or Cl₂ is a diatomic halogen with the atomic number of 17. 

In biological terms, chlorine is found as a Cl^- ion, or chloride ion in cells. 

Sodium Chloride (NaCl) is the compound in which chlorine is most frequently found in the body. Chloride concentration plays a vital role in epithelial tissues, and NaCl is the salt produced in the sweat glands.