Consider the following statements about the boiling points of haloalkanes and haloarenes.
(A) The boiling points of chlorides, bromides and iodides are considerably higher than those of hydrocarbons of comparable molecular mass.
(B) Methyl chloride, methyl bromide and ethyl chloride are gases at room temperature.
(C) The boiling points of isomeric haloalkanes increase with increase in branching.
(D) The boiling points of isomeric dihalobenzenes are very nearly the same.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
Boiling points depend on the intermolecular forces (dipole-dipole and van der Waals) that must be overcome when a liquid boils.
(A) The boiling points of chlorides, bromides and iodides are considerably higher than those of hydrocarbons of comparable molecular mass. — True. Haloalkanes are polar and heavier than the parent hydrocarbon, so their intermolecular attractions are stronger.
(B) Methyl chloride, methyl bromide and ethyl chloride are gases at room temperature. — True. These small molecules boil below room temperature; higher members are liquids or solids.
(C) The boiling points of isomeric haloalkanes increase with increase in branching. — False. They decrease with branching. Among the isomeric bromobutanes, 2-bromo-2-methylpropane, the most branched, has the lowest boiling point.
(D) The boiling points of isomeric dihalobenzenes are very nearly the same. — True. The o-, m- and p-isomers boil at almost the same temperature; they differ in their melting points, which are highest for the para-isomer.
NCERT (2026-27 edition):
6.6 Physical Properties – “Methyl chloride, methyl bromide, ethyl chloride and some chlorofluoromethanes are gases at room temperature. Higher members are liquids or solids.” … “Due to greater polarity as well as higher molecular mass as compared to the parent hydrocarbon, the intermolecular forces of attraction (dipole-dipole and van der Waals) are stronger in the halogen derivatives. That is why the boiling points of chlorides, bromides and iodides are considerably higher than those of the hydrocarbons of comparable molecular mass.”
“The boiling points of isomeric haloalkanes decrease with increase in branching. For example, 2-bromo-2-methylpropane has the lowest boiling point among the three isomers.”
“Boiling points of isomeric dihalobenzenes are very nearly the same. However, the para-isomers are high melting as compared to their ortho- and meta-isomers.”