The table gives the densities of some haloalkanes.
Each of the following haloalkanes is shaken with water, and the mixture is left to stand. Which one forms the upper layer, above the water? (Density of water = 1.0 g/mL)
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → n–C3H7Cl
Haloalkanes are only very slightly soluble in water, so each one stays as a separate layer, and a liquid less dense than water floats on top. The table gives 0.89 g/mL for n–C3H7Cl, the only value below 1.0, so it forms the upper layer; bromo and polychloro compounds are heavier than water and sink below it.
Why the other options are incorrect
Option (1) n–C3H7Br — Incorrect. Its density is 1.335 g/mL, above 1.0; it is a bromo derivative and forms the lower layer.
Option (2) CH2Cl2 — Incorrect. Its density is 1.336 g/mL, above 1.0; with two chlorine atoms it is a polychloro derivative and sinks below the water.
Option (4) CHCl3 — Incorrect. Its density is 1.489 g/mL, above 1.0; with three chlorine atoms it is heavier still and forms the lower layer.
NCERT (2026-27 edition):
6.6 Physical Properties – “Density … Bromo, iodo and polychloro derivatives of hydrocarbons are heavier than water. The density increases with increase in number of carbon atoms, halogen atoms and atomic mass of the halogen atoms (Table 6.3).”
“Solubility … The haloalkanes are very slightly soluble in water.”
Table 6.3: Density of Some Haloalkanes