The increasing order of boiling points of all these compounds of comprable molecular masses is :
`underset((213K))(CH_(3)CH_(2)CH_(3))ltunderset((249K))(CH_(3)OCH_(3))ltunderset((293K))(CH_(3)CHO)ltunderset((351K))(CH_(3)CH_(2)OH)`
Explanation : We know that the boiling points of liquids are directly related to the magnitude of the intermolecular forces of attraction.
(i) Hydrocarbons (alkanes) are completley non-polar. The only attractive forces in their molecules are Van der Waals forces which are quite weak. That is why propane `(CH_(3)CH_(2)CH_(3))` has the least boiling point. It is a gas at room temperature.
(ii) Ethers have bent strucutres and are also polar. However, there is no hydrogen bonding in their molecules. The only attractive forces are dipolar forces. Therefore, boiling point of dimethyl ether `(CH_(3)OCH_(3))` is higher than that of propane. However, it is also a gas at room temperature.
(iii) Aldehydes contain polar carbonyl group and have strong dipolar interctions in their molecules. It is more than in ethers. Therefore, the boiling point of acetaldehyde `(CH_(3)CHO)` is more than that of dimethyl ether.
(iv) Out of all the families listed, alcohols have maximum intermolecular forces in the form of hydrogen bonding
As a result, ethyl alcohol `(C_(2)H_(5)OH)` has the maximum boiling point.
