Chlorine, which at normal conditions is a yellow-green Cl₂ gas, is a very caustic substance. Elemental chlorine corrodes nearly every metal and is toxic for every creature. In nature, it always occurs in compounds, the most famous of those is sodium chloride, NaCl, which is table salt. Chloride is a vitalpart of the body. The compound of Hydrogen and Chlorine, HCl, dissolved in water, gives hydrochloric acid. Chlorine also is part of the very common plastic PVC.