A chemical element with the symbol Cl and the atomic number 17 is ‘Chlorine’. It is the second-lightest of the halogens that appears between fluorine and bromine in the periodic table and its properties are median between them. At room temperature, it is a yellow-green gas. Also, it has two stable isotopes, 35Cl and 37Cl. These are the only two natural isotopes occurring in quantity, with 35Cl making up 76% of natural chlorine and 37Cl making up the remaining 24%.