The correct increasing order of boiling points is ‌
CH3CH2CH3
(III)
<
CH3−O
‌ (I) ‌
−‌
CH3
‌ (II) ‌
<‌
CH3CHO
‌ (IV) ‌
<‌
CH3OH
CH3
It is because of strength of intermolecular forces present in each molecule, with hydrogen bonding in alcohols being the strongest and van der Waals' forces in alkanes being the weakest.
