n-Butylamine (I), diethylamine (II) and N,N-dimethylethyl amine (III) have the same molar mass. The increasing order of their boiling point is

Step-by-step solution

H 3 C - C H 2 - C H 2 - C H 2 - N H 2 n-butylamine primary amine C H 3 C H 2 - N H - C H 2 - C H 3 Diethylamine Secondary amine C H 3 - N | - C 2 H 5 C H 3 ethyldimethylamine ( tertiary amine ) Primary amines have two hydrogen atoms available for hydrogen bond formation, while 2 ° amines have only one hydrogen atom for hydrogen bond formation. 3 ° amines do not have intermolecular association due to absence of hydrogen atom. Thus, order of boiling point of isomeric amines is as follows 3 ° < 2 ° < 1 ° or I I I < I