The first thing to consider is the properties of sulfur dioxide. Sulfur dioxide is a simple molecule. It contains only three atoms which means it is small, and very strong covalent bonds connect these. Remember a covalent bond is where two atoms share a pair of electrons, and a large amount of energy is required to break covalent bonds. Between the sulfur dioxide molecules there are weak forces which we call intermolecular forces, because sulfur dioxide is a small molecule, these interactions are weak. When sulfur dioxide is boiled, it is the weak intermolecular forces which are broken and not the strong covalent bonds. Only a small of amount of energy is required to break the intermolecular forces so the boling point is low. For an exam answer you would need to state that sulfur dioxide is a small molecule (1 mark) so it has weak intermolecular forces between molecules (1 mark) therefore only a small amount of energy is required to seperate the molecules of sulfur dioxide (1 mark) so it has a low boiling point.