The molecular masses of the given compounds are in the range of 44-66 g/mol. The second molecule, CH₃CH₂OH contains OH alcoholic group due to which it undergoes extensive H bonding with each other, leading to the association of the molecules. Therefore it has a highest boiling point. In the molecule CH₃CHO , there is strong intermolecular dipole-dipole attraction due to presence of -CHO aldehydic group( as H will have partial positive charge and oxygen will have partial negative charge , so there will attraction between molecules),which is weak in case of CH₃OCH₃ as both CH₃ groups have +I effect which results in decrease in electron affinity for the oxygen attached to it( with no partially positive H atom). And in CH₃CH₂CH₃ there are only weak van der Waals forces of attraction. So the compounds in increasing order of their boiling point are:

CH₃CH₂CH₃<CH₃OCH₃<CH₃CHO<CH₃CH₂OH.