The dipole moment of o, p and m-dichlorobenzene will be in the order :

The dipole moment of p – dichlorobenzene is zero because of symmetrical structure.

 o-dichlorobenzene has a higher dipole moment due to a lower bond angle than the m-isomer. Hence, the order of increasing dipole moment is :
P –dichlorobenzene  < m –dichlorobenzene  <  o –dichlorobenzene