Hydrogen Iodide (HI) is a diatomic molecule. Aqueous solutions of HI are known as Iohydroic Acid or hydroiodic Acid, a strong Acid. Gas and aqueous solution are interconvertible. Hydrogen Iodide is used in organic and inorganic synthesis as one of the primary sources of iodine and as a reducing agent.
Hydriodic acid can be used to synthesize Sodium iodide or Potassium iodide for increasing iodine content of salt. Hydriodic acid is one of the strongest of all the common halide acids due to the high stability of its corresponding conjugate base.