Final answer:
In comparing the boiling points of substances based on their intermolecular forces, we find that n-butane, sulfur dioxide (SO2), and phosgene have higher boiling points in their respective pairs due to stronger London dispersion forces, dipole-dipole interactions, and higher molecular masses.
Step-by-step explanation:
The question asks us to identify the type of intermolecular forces present in each substance and determine which substance has the higher boiling point:
Propane (CH3CH2CH3) or n-butane (CH3CH2CH2CH3): Both compounds are nonpolar alkanes, so the primary intermolecular force is London dispersion forces. These forces are generally stronger in molecules with higher molecular mass and a larger surface area. Since n-butane has both a higher molecular mass and a larger surface area than propane, it has the higher boiling point.
Krypton or sulfur dioxide (SO2): Krypton is a noble gas and only has very weak London dispersion forces, while SO2 is a polar molecule that exhibits dipole-dipole interactions in addition to London dispersion forces. Therefore, SO2, with its stronger intermolecular forces, has the higher boiling point.
Phosgene (Cl2CO) or formaldehyde (H2CO): Both molecules are polar, but phosgene has larger dipole moments due to the presence of two chlorine atoms, and its molecular mass is significantly higher than that of formaldehyde. Consequently, phosgene exhibits stronger intermolecular forces and has a higher boiling point.