The term "Cl-" refers to the chloride ion, which is a negatively charged ion formed when chlorine (Cl) gains an electron. Chloride is commonly found in nature, especially in salt (NaCl), where it pairs with sodium. It plays a crucial role in various biological processes, including maintaining fluid balance in cells and transmitting nerve impulses. Chloride ions are essential for human health, as they help regulate blood pressure and support digestion by forming hydrochloric acid in the stomach. Additionally, chloride is important in industrial applications, such as water treatment and the production of chemicals like chlorine gas (Cl2).