The correct chemical formula for Hypobromous acid is option 2: HOBr.

Let`s analyze each option to better understand why it is the correct answer.

Option 1: HBrO4. This formula represents Perbromic acid, not Hypobromous acid. The prefix "Per-" indicates that there are more oxygen atoms in the compound.

Option 2: HOBr. This formula represents Hypobromous acid. It consists of the elements hydrogen (H), oxygen (O), and bromine (Br). The subscript "O" indicates that there is one oxygen atom, and the absence of any subscripts for hydrogen and bromine suggests that there is only one atom of each in the compound. Therefore, this option is the correct chemical formula for Hypobromous acid.

Option 3: HBr. This formula represents Hydrobromic acid, not Hypobromous acid. Hydrobromic acid is a strong acid composed of hydrogen and bromine.

Option 4: HBrO3. This formula represents Bromic acid, not Hypobromous acid. Bromic acid is a strong acid composed of hydrogen, bromine, and three oxygen atoms.

In conclusion, option 2: HOBr is the correct