HBr is the formula for hydrobromic acid, which also goes by the name hydrogen bromide. Hydrobromic acid has a boiling point of 122 degrees Celsius and exists as a liquid at room temperature (25 degrees Celsius).
Hydrobromic acid is classified as a strong acid and completely dissociates into its individual hydrogen and bromide ions in water. There are only seven acids recognized to be strong acids. In addition to hydrobromic acid, these are hydroiodic acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid and chloric acid. Of these, hydroiodic acid is the strongest acid with a pKa of -10. Hydrobromic acid is the second strongest acid in this set with a pKa of -9.