Aryl chlorides are prepared by electrophilic substitution of arenes with chlorine in the presence of iron(III) chloride. The ortho and para isomers formed in such a reaction can be separated easily because of a large difference in their
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → melting points
The boiling points of such isomers are very nearly the same, but their melting points differ a lot. The para isomer is more symmetrical, fits better into the crystal lattice and so melts at a much higher temperature. On cooling, the para isomer crystallises out and can be removed from the ortho isomer.
Why the other options are incorrect
Option (1) densities — Incorrect. Density depends on the number of carbon and halogen atoms and the mass of the halogen, which are the same in both isomers.
Option (2) boiling points — Incorrect. The boiling points of such position isomers are very nearly the same, so they cannot be separated easily by distillation.
Option (4) solubilities in water — Incorrect. Both isomers are only very slightly soluble in water, so solubility in water does not separate them.
NCERT (2026-27 edition):
6.5 Preparation of Haloarenes – “The ortho and para isomers can be easily separated due to large difference in their melting points.”
6.6 Physical Properties – “…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.”