Which of the following has 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 moments. In CHCl₃, the resultant of two C—Cl dipoles is opposed by the result of C—H and C—Cl bond. Since the latter resultant is expected to be smaller than the former, CHCl₃ has a finite dipole (1.03 D) moment.

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

Thus, CH₂Cl₂ has the highest dipole moment.