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HClO2, a monobasic acid, in which chlorine has an oxidation state of +3. Chlorous acid exists only in dilute aqueous solutions. Its dissociation constant is 1.1 × 10–2 at l8°C. The acid is produced by dissolving chlorine dioxide in water: 2ClO2 + H2O = HClO2 + HClO3. Salts of chlorous acid (chlorites), mainly sodium chlorite, NaClO2, are used in industry.