$\underset{1.64\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{I}}<\underset{1.79\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{B}\mathrm{r}}<\underset{1.84\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{F}}<\underset{1.94\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}}$
The charge separation in $\mathrm{C}-\mathrm{X}$ bond decreases in the order
$\mathrm{C}-\mathrm{F}>\mathrm{C}-\mathrm{C}\mathrm{l}>\mathrm{C}-\mathrm{B}\mathrm{r}>\mathrm{C}-\mathrm{I},$ due to decrease in the electronegativity as we more from $\mathrm{F}\to \mathrm{C}\mathrm{l}\to \mathrm{B}\mathrm{r}\to \mathrm{I}$ .
$\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}$ has higher dipole moment than $\mathrm{C}{\mathrm{H}}_3\mathrm{F}$ , because of larger bond length of $\mathrm{C}-\mathrm{C}\mathrm{l}$ bond. The larger $\mathrm{C}-\mathrm{C}\mathrm{l}$ bond length causes dipole moment $\left(\mathrm{\mu }\right)=\mathrm{q}\times \mathrm{d}$ to be larger for $\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}$ than $\mathrm{C}{\mathrm{H}}_3\mathrm{F}$ . In case of other haloalkanes, the effect of larger $\mathrm{C}-\mathrm{X}$ bond length cannot outweigh the effect of decreased charge separation.