Arrange in the order of increasing dipole moment 
I) toluene 
II) m- dichlorobenzene 
III) o- dichlorobenzene 
IV) p- dichlorobenzene

The increasing order of dipole moment is IV<I<II<III.

o−, m−, p− derivates has α=60^o, 120^o and 180^o and thus, resultant vector has zero dipole moment in p-derivative because of symmetrical structure. Also dipole moment of m-dichlorobenzene is more than toluene. o− and m−dichlorobenzene have higher dipole moments than toluene due to high electronegativity of chlorine than CH₃​ group. Further, to the o-dichlorobenzene has higher dipole moment due to lower bond angle than the m-isomer.