An anion is a type of ion that carries a negative charge. This occurs when an atom or molecule gains one or more electrons, resulting in an excess of negatively charged particles. Anions are commonly found in various chemical compounds, such as salts, where they balance the positive charge of cations, which are positively charged ions. Anions play a crucial role in many chemical reactions and processes. For example, in electrolytes, anions help conduct electricity in solutions. Common examples of anions include chloride (Cl⁻), sulfate (SO₄²⁻), and nitrate (NO₃⁻), each of which has specific functions in biological and environmental systems.