Match List-I with List-II.
| List-I (Observation) | List-II (Reason) |
|---|---|
| (A) Chlorides, bromides and iodides boil at much higher temperatures than hydrocarbons of comparable molecular mass. | (I) Its symmetrical molecules fit into the crystal lattice better. |
| (B) For the same alkyl group, the boiling points are in the order RI > RBr > RCl > RF. | (II) Greater polarity and higher molecular mass make the intermolecular forces stronger. |
| (C) 1,4-Dichlorobenzene has a higher melting point than 1,2- and 1,3-dichlorobenzene. | (III) The new attractions formed with water molecules are weaker than the hydrogen bonds broken in water. |
| (D) Haloalkanes are only very slightly soluble in water. | (IV) The van der Waals forces become stronger as the size and mass of the halogen atom increase. |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-II, B-IV, C-I, D-III
(A) Chlorides, bromides and iodides boil at much higher temperatures than hydrocarbons of comparable molecular mass. — This matches (II) Greater polarity and higher molecular mass make the intermolecular forces stronger. The C–X bond makes the molecule polar, so dipole-dipole attractions add to the van der Waals forces, and the halogen also adds mass.
(B) For the same alkyl group, the boiling points are in the order RI > RBr > RCl > RF. — This matches (IV) The van der Waals forces become stronger as the size and mass of the halogen atom increase. The alkyl group is the same in all four, so the difference comes from the halogen: a larger and heavier halogen atom gives stronger van der Waals forces and a higher boiling point.
(C) 1,4-Dichlorobenzene has a higher melting point than 1,2- and 1,3-dichlorobenzene. — This matches (I) Its symmetrical molecules fit into the crystal lattice better. 1,4-Dichlorobenzene is the para-isomer; its symmetry lets the molecules pack closely in the solid.
(D) Haloalkanes are only very slightly soluble in water. — This matches (III) The new attractions formed with water molecules are weaker than the hydrogen bonds broken in water. Less energy is released than is needed to separate the molecules, so little haloalkane dissolves.
NCERT (2026-27 edition):
6.6 Physical Properties – “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.”
“…For the same alkyl group, the boiling points of alkyl halides decrease in the order: RI> RBr> RCl> RF. This is because with the increase in size and mass of halogen atom, the magnitude of van der Waal forces increases.”
“…However, the para-isomers are high melting as compared to their ortho- and meta-isomers. It is due to symmetry of para-isomers that fits in crystal lattice better as compared to ortho- and meta-isomers.”
“The haloalkanes are very slightly soluble in water. … Less energy is released when new attractions are set up between the haloalkane and the water molecules as these are not as strong as the original hydrogen bonds in water. As a result, the solubility of haloalkanes in water is low.”