The higher halogens form acids which are completely ionized in water up to a point. Surprisingly that point is the same for each of the acids. When there are just five water molecules for each HCl, HBr or HI, these hydrohalic acids stop dissolving in water and thus stop ionizing. The water is said to be saturated with HX and no more will dissolve. Because of the weight of the halogen atoms differ, concentrated hydrochloric acid is ~36 weight percent, while hydrobromic acid is 48% HBr and hydriodic acid is ~57% HI. But each of those solutions has just five water molecules for each molecule of HX dissolved. These concentrated acids are commercially available from a chemical supply house.