Consider the following statements about the physical properties of organohalogen compounds.
(A) Methyl chloride, methyl bromide and ethyl chloride are gases at room temperature.
(B) The para-isomers of dihalobenzenes have lower melting points than their ortho- and meta-isomers.
(C) Haloalkanes are very slightly soluble in water because the new attractions set up between haloalkane and water molecules are not as strong as the original hydrogen bonds in water.
(D) Bromo, iodo and polychloro derivatives of hydrocarbons are lighter than water.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) and (D) only
The physical properties of organohalogen compounds come from the polar C–X bond and from the large mass of the halogen atoms.
(A) Methyl chloride, methyl bromide and ethyl chloride are gases at room temperature. — Correct statement. These lower members are gases; the higher members are liquids or solids.
(B) The para-isomers of dihalobenzenes have lower melting points than their ortho- and meta-isomers. — Incorrect statement. The para-isomers are high melting. Their symmetry lets them fit into the crystal lattice better than the ortho- and meta-isomers. (Their boiling points are very nearly the same.)
(C) Haloalkanes are very slightly soluble in water because the new attractions set up between haloalkane and water molecules are not as strong as the original hydrogen bonds in water. — Correct statement. Energy is needed to break the hydrogen bonds in water, and less energy is released when the weaker haloalkane–water attractions form, so little dissolves.
(D) Bromo, iodo and polychloro derivatives of hydrocarbons are lighter than water. — Incorrect statement. They are heavier than water. Density rises with the number of carbon atoms, the number of halogen atoms and the atomic mass of the halogen.
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.”
“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. It is due to symmetry of para-isomers that fits in crystal lattice better as compared to ortho- and meta-isomers.”
“Bromo, iodo and polychloro derivatives of hydrocarbons are heavier than water.”
“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.”