$CHCl_3$ has the highest dipole moment. The reason for it can be understood by looking into the structure of the given compounds. (i) $CH_2Cl_2$ has a symmetrical structure such that the $C- Cl$ bond dipole moments cancel out each other while the$C -H$ dipole moments reinforce each other and thus contribute to a net moment.(ii) $CCl_4$ has a perfectly tetrahedral structure where the net dipole of 3 C – Cl bonds point in a direction opposite to the fourth C – Cl bond and thus results in zero dipole moment.(iii) In $CHCl_3$ net moment of $3C – Cl$ reinforces the dipole moment of $C – H$ and therefore has the highest dipole moment.