In the case of hydrogen bromide (HBr), the predominant intermolecular force is dipole-dipole interaction.
Here’s why: HBr is a polar molecule due to the significant electronegativity difference between the hydrogen and bromine atoms. Bromine is more electronegative than hydrogen, which creates a dipole moment in the molecule. The positive end of one HBr molecule is attracted to the negative end of another HBr molecule, leading to dipole-dipole interactions.
While London dispersion forces are present in all molecules, they are generally weak and are more dominant in nonpolar or lighter molecules. Hydrogen bonding also does not apply here because HBr does not contain hydrogen bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine, which is essential for hydrogen bonds to form.
Therefore, among the options given: a) London dispersion, b) dipole-dipole, and c) hydrogen bonding, the correct answer is b) dipole-dipole.