Dipole moment is highest for

As the number of chlorine atoms increases symmetrical nature increases

μ of CH₃Cl>CH₂Cl₂>CHCl₃>CCl₄
Alternate Explanation
CCl₄ is a symmetrical molecule with zero dipole movement
 CH₃Cl,CH₂Cl₂,CHCl₃  have distorted tetrahedral shape. As the number of 'Cl' atoms increases repulsions between bond pairs increases thus bond angle (θ) increases.
Dipole moment decreases.