Explain why hydrogen bromide has a higher boiling point than hydrogen chloride.

Hydrogen bromide and hydrogen chloride are both simple molecules. They have London forces between molecules. It is essential that you highlight that these interactions (induced dipole-dipole) are BETWEEN the molecules rather than WITHIN them. Boiling point is determined by the energy required to break these intermolecular forces. Therefore, stronger intermolecular forces between molecules will lead to a higher boiling point as more energy is required.The only difference between HBr and HCl are the sizes of the halogen atom. Br is larger, meaning that it has more electrons. More electrons mean that when the electrons move randomly, a more strong dipole can be induced in the neighbouring molecules. This means there are more interactions between the larger HBr molecules than between the smaller HCl molecules.In this question, the focus is on intermolecular forces- a common mistake is to go down a rabbit hole talking about the covalent bonds within the molecule, which are not involved in boiling point determination at A-level.