Define anion.

Define anion.

• A. A neutral molecule
• B. A positively charged ion
• C. A negatively charged ion
• D. An ion with a charge that changes with pH

Answer: (C)

An anion is a negatively charged ion. It forms when an atom or molecule gains one or more extra electrons, giving it a net negative charge. In water treatment contexts, common anions include chloride (Cl−), sulfate (SO4^2−), and nitrate (NO3−). Because it carries a negative charge, anions move toward the positive electrode in an electrical field and are written with a minus sign. This is different from a neutral molecule, which has no net charge, and from a positively charged ion, which is a cation. A charge that changes with pH isn’t the defining feature of anions; some species can exist in multiple protonation forms, but anions are defined by their net negative charge.

An anion is a negatively charged ion. It forms when an atom or molecule gains one or more extra electrons, giving it a net negative charge. In water treatment contexts, common anions include chloride (Cl−), sulfate (SO4^2−), and nitrate (NO3−). Because it carries a negative charge, anions move toward the positive electrode in an electrical field and are written with a minus sign. This is different from a neutral molecule, which has no net charge, and from a positively charged ion, which is a cation. A charge that changes with pH isn’t the defining feature of anions; some species can exist in multiple protonation forms, but anions are defined by their net negative charge.