Dipole moment is inversely proportional to angle of separation. Thus smaller angle of separation will cause large dipole moment whereas large angle of separation causes less dipole moment. I>II>III
I. (I) has a smaller angle of separation between two Br atoms than in (II) and (III), resulting in more net dipole moment (µ).
II. (II) has a large angle of separation between two Br atoms; therefore, net (µ) is less than (I).
III. In (III), two Br atoms and two H atoms have equal and opposite bond moments; therefore, the net µ is zero.
