Chlorine is prepared on a large scale by the electrolysis of concentrated sodium chloride solution. In this process, electricity is passed through a solution of sodium chloride, which leads to the breakdown of salt into its constituent ions, namely sodium and chloride. The chloride ions then react at the anode, producing chlorine gas. This process is used to produce large quantities of chlorine, which is an important industrial chemical used in a variety of applications such as water treatment, disinfection, and the production of various chemicals.