Hydrogen iodide (HI) is adiatomic molecule. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, astrong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under standard conditions; whereas, the other is an aqueous solution of said gas. They are interconvertible. HI is used inorganicandinorganic synthesisas one of the primary sources ofiodineand as areducing agent.