With an increase in the molecular weight, the boiling point increases. With an increase in OH groups, the extent of hydrogen bonding increases, and boiling point increases.Due to above two reasons, (IV) Hydroxybenzene has a lowest boiling point.In case of (I) 1,2-dihydroxybenzene, since two OH groups are in the ortho position, there is intramolecular hydrogen bonding. In (II) 1,3-dihydroxybenzene and (III) 1,4-dihydroxybenzene, intermolecular hydrogen bonding is present which leads to the molecular association. Hence (I) 1,2-dihydroxybenzene has a lower boiling point than (II) 1,3-dihydroxybenzene and (III) 1,4-dihydroxybenzene.The increasing order of boiling points of above-mentioned alcohols is (IV) Hydroxybenzene < (I) 1,2-dihydroxybenzene < (II) 1,3-dihydroxybenzene < (III) 1,4-dihydroxybenzene.