Final answer:
Compound A, propane (CH₃CH₂CH₃), has the lowest boiling point among the given substances as it can only exhibit London dispersion forces, which are the weakest intermolecular forces.
Step-by-step explanation:
The substances listed are organic compounds with similar molar masses, which means we need to look at the types of intermolecular forces present to determine their boiling points.
Compound A, CH₃CH₂CH₃ (propane), is a nonpolar hydrocarbon and will have only London dispersion forces, which are the weakest intermolecular forces. Compound B, CH₃OCH₃ (dimethyl ether), is slightly polar and will exhibit both London dispersion forces and dipole-dipole interactions.
Compound C, CH₃CH₂OH (ethanol), possesses an -OH group and can engage in hydrogen bonding, which is much stronger than the other types of intermolecular forces.
Compound D, CH₃CHO (acetaldehyde), has a polar carbonyl group but lacks the ability to engage in hydrogen bonding like ethanol.
Among these, the compound with only London dispersion forces, CH₃CH₂CH₃ (propane), would have the lowest boiling point.