An anion is a negatively charged ion that forms when an atom or molecule gains one or more electrons. This extra negative charge results in an imbalance between the number of protons and electrons, leading to a net negative charge. Anions play a crucial role in various chemical reactions and are essential in the formation of ionic compounds. Common examples of anions include chloride (Cl⁻), sulfate (SO₄²⁻), and nitrate (NO₃⁻). Anions are often found in salts, where they pair with positively charged ions called cations. Together, anions and cations create stable compounds that are important in biological systems and industrial applications.