Which of the following alkyl halide requires the largest enthalpy to dissociate C-X bond ?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → CH3 − F
The strength of the carbon–halogen bond depends on how well the carbon orbital overlaps with the halogen orbital. Going down the group from F to I, the halogen atom becomes larger, the C–X bond becomes longer and the overlap becomes weaker. So the bond enthalpy decreases from C–F to C–I:
\( \displaystyle \ce{C-F} > \ce{C-Cl} > \ce{C-Br} > \ce{C-I}\quad(\text{bond enthalpy}) \)
So CH3–F, with the shortest and strongest C–X bond (452 kJ mol−1), needs the largest enthalpy to break it.
NCERT (2026-27 edition):
Nature of C-X Bond – …
