Correct Answer: D
Explanation:
Melting and boiling points are dependent on the attraction between molecules. The strength of the intermolecular attractions - hydrogen bonding, dipole-dipole attraction, and London dispersion forces - determine the boiling point.
There are three are aldehydes and one ketone. All posses a net dipole moment, and some dipole-dipole interaction. In addition, there will be some London dispersion forces. The substance with the highest boiling point will be the one with the dipole-dipole attraction plus the greatest London dispersion forces. Since London dispersion forces are based on the total number of electrons and the volume over which they are spread, then the ketone will have the highest boiling point.
Methanal -- formaldehyde boils at -21 C
ethanal -- acetaldehyde boils at 20 C
propanal -- boils at 48 C
2 hexanone -- 128 C