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Perchloric acid, HClO<sub>4</sub>, is an oxoacid of chlorine and is a colorless liquid soluble in water. It is a strong acid like sulfuric acid or nitric acid. It is a superacid, but it is not the strongest Brønsted-Lowry acid (which is fluoroantimonic acid, HFSbF<sub>5</sub>). Its pKa is −7[1].