Arrange the alkyl halides in order of their increasing boiling points.
(A) Methyl chloride
(B) Methyl bromide
(C) Methyl iodide
(D) Methyl fluoride
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (D), (A), (B), (C)
For the same alkyl group, the boiling point rises with the size and mass of the halogen atom, because larger molecules have stronger van der Waals forces:
So the boiling point rises with the atomic mass of the halogen:
\( \displaystyle \text{R-F} < \text{R-Cl} < \text{R-Br} < \text{R-I} \)
\( \displaystyle \ce{CH3F} < \ce{CH3Cl} < \ce{CH3Br} < \ce{CH3I} \)
Matching the given compounds:
(D) Methyl fluoride: \( \ce{CH3F} \), b.p. −78.4 °C
(A) Methyl chloride: \( \ce{CH3Cl} \), b.p. −24.2 °C
(B) Methyl bromide: \( \ce{CH3Br} \), b.p. 3.6 °C
(C) Methyl iodide: \( \ce{CH3I} \), b.p. 42.4 °C
Shortcut: Methyl fluoride (D) has the lowest boiling point and methyl iodide (C) the highest. Only Option (3) starts with (D) and ends with (C).
NCERT (2026-27 edition):
Physical Properties – …
