The correct sequence of bond enthalpy of ‘C–X’ bond is :

The correct option is CH₃ – F > CH₃ – Cl > CH₃ – Br > CH₃ – I.

Bond enthalpy (also known as bond dissociation energy) is the energy required to break one mole of a specific bond. The strength of the carbon-halogen (C–X) bond depends directly on the bond length and the orbital overlap between carbon and the halogen atom:

1. Atomic Size Trend: As we move down Group 17 (halogens) in the periodic table from fluorine to iodine, the size of the halogen atom increases in the order:
F < Cl < Br < I

2. Orbital Overlap: The carbon atom forms the C–X bond using its 2p orbital. The halogen atom uses its valence p-orbital (2p for F, 3p for Cl, 4p for Br, and 5p for I). As the valence shell size of the halogen increases, the overlap between carbon's 2p orbital and the halogen's valence orbital becomes increasingly diffuse and less effective.

3. Bond Length and Strength: A less effective orbital overlap results in a longer and weaker bond. Therefore, bond length increases in the order:
C–F < C–Cl < C–Br < C–I

Since shorter and stronger bonds require more energy to break, the bond enthalpy is inversely proportional to the bond length. Thus, the bond enthalpy decreases in the order:
${\text{CH}}_3-\text{F}>{\text{CH}}_3-\text{Cl}>{\text{CH}}_3-\text{Br}>{\text{CH}}_3-\text{I}$