Which one of the following has the highest dipole moment?

(i) CH2Cl2 (ii) CHCl3 (iii) CCl4

The three dimensional structures of the three compounds along with the direction of dipole moment in each of their bonds are given below:-

CCl4 being symmetrical has zero dipole moment. In CHCl3, the resultant of the two C-Cl dipole moments is opposed by the resultant of C-H and C-Cl bonds. Since the dipole Moment of latter resultant is expected to be smaller than the former,CHCl3 has a finite dipole moment(1.03D)

In CH2Cl2, the resultant of two C-Cl dipole moments is reinforced by resultant of two C-H dipoles. Therefore, CH2Cl2(1.62D) has a dipole moment higher than that of CHCl3. Thus ,CH2Cl2 has the highest dipole moment.