n – pentane = A, Diethyl ether = B, Butanal = C, n – butylalcohol =  D. Correct increasing order of boiling point is

B < A < C < D.Inter molecular hydrogen bonding in alcohols.Dipole-dipole attractions in carbonyl compounds.Though in ethoxy ethane the attractions are dipole-dipole, they are weaker than London forces in n-pentane.