Answer :
CH3CH2CH2CH3 < CH3OCH2CH3 < CH3CH2NH2 < CH3CH2OH is the increasing order of boiling point.
Explanation:
The boiling point of a compound depends on intermolecular forces as vander waals, hydrogen bonding and ionic bonds. The hydrogen bond is the strongest one.
The intensity of these forces depends on the functional group in the compound.
The hydrogen bonding in CH3CH2OH is strong as it is double bond between oxygen and hydrogen. This causes a rise in boiling point of this compound.
CH3CH2NH2 has amide group, it is having less boiling point than CH3CH2OH because nitrogen is less electronegative than oxygen so forms less strong hydrogen bonds.
CH3OCH2CH3 is an ether and it does not form hydrogen bonds and have weaker vander waal forces
CH3CH2CH2CH3 is having least boiling point because it does not have any polar atom and has only London dispersion forces hence low boiling point.