The alkyl halide which possess highest dipole moment is

${\mathrm{CH}}_3\mathrm{Cl}>{\mathrm{CH}}_3\mathrm{F}>{\mathrm{CH}}_3\mathrm{Br}>{\mathrm{CH}}_3\mathrm{I}$

$\mathrm{\mu } = \mathrm{e} \times \mathrm{d}$

though C-F bond is more polar than C-Cl bond; C-Cl bond length is more than C-F bond 

${(\mathrm{e}\times \mathrm{d})}_{{\mathrm{CH}}_3\mathrm{Cl} }> {(\mathrm{e}\times \mathrm{d})}_{{\mathrm{CH}}_3\mathrm{F}}$