Chlorine (from Greek χλωρός, chloròs, "pale green") is the chemical element of the periodic table with atomic number 17 and symbol Cl. It is part of the halogen group, located in group 17 of the periodic table. The chlorine gas is yellowish green, two and a half times heavier in air, has a stifling odor that is extremely unpleasant and is very poisonous. Under standard conditions and in a wide range of temperatures and pressures, chlorine gas is made up of a biatomic Cl2 molecule (CAS number 7782-50-5). It is a powerful oxidizing, whitening and disinfecting agent. In the form of chloride anion Cl- is a component of the common kitchen salt (or sodium chloride) and many other compounds, it is very abundant in nature and necessary for almost all forms of life, including the human organism (blood Human contains in fact a fair amount of chloride anion).
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