The molecule having largest C-X bond length is

The correct answer is Option (2) → $CH_3-I$

The C–X bond length in methyl halides (CH₃X) increases as we go down the group in the periodic table (F → Cl → Br → I). This is due to the increasing atomic size (atomic radius) of the halogen atom.

Atomic radii order: F < Cl < Br < I

Thus, the covalent bond length order: C–F < C–Cl < C–Br < C–I

CH₃−I has the largest C–X bond length.