It is an aqueous solution of hydrogen iodide with the chemical formula HI(aq).
It is a strong acid, in which hydrogen iodide is ionized completely in an aqueous solution.
[2] Hydroiodic acid reacts with oxygen in air to give iodine: Like hydrogen halides, hydroiodic acid adds to alkenes to give alkyl iodides.
It can also be used as a reducing agent, for example in the reduction of aromatic nitro compounds to anilines.
[4][5] Hydroiodic acid is listed as a U.S. Federal DEA List I Chemical, owing to its use as a reducing agent related to the production of methamphetamine from ephedrine or pseudoephedrine (recovered from nasal decongestant pills).