Arrange the following compounds in order of increasing dipole moment : toluene (I), m-dichlorobenzene (II), o-dichlorobenzene (III), p-dichlorobenzene (IV)

μres = μ12 + μ22 + 2μ1 μ2  cos θOut of (II) and (III) ‘O’ isomer has more dipole moment.The increasing order of dipole-moment is :p-dichlorobenzene < toluene < m-dichlorobenzene < o-dichlorobenzene.