For the compounds CH 3 Cl, CH 3 Br, CH 3 I and CH 3 F, the correct order of increasing C-halogen bond length…

C-halogen bond length totally depends on the electronegativity difference between Carbon and halogen. The more the difference and the less is the bond length. The electronegativity order of halogens is $\mathrm{I}<\mathrm{Br}<\mathrm{Cl}<\mathrm{F}$. Hence, the correct order of increasing C-halogen bond length is $\mathrm{CH}3\mathrm{F}<\mathrm{CH}3\mathrm{Cl}<\mathrm{CH}3\mathrm{Br}<\mathrm{CH}3\mathrm{I}.$

Or we can say that as the size of halogen increases C-halogen bond length also increases.