The acid whose formula is HI is called hydroiodic acid.
Hydroiodic acid is a strong acid that is formed when hydrogen iodide gas is dissolved in water. Its structure consists of hydrogen (H) and iodine (I) atoms, making it part of the hydrogen halides family. When hydroiodic acid is in solution, it dissociates completely into hydrogen ions (H+) and iodide ions (I–), which is what gives it its strong acidic properties. It is often used in organic synthesis and for various laboratory applications due to its ability to donate protons easily.