Explain why the dipole moment of chlorobenzene is lower than cyclohexyl chloride ?

There are two major aspects that can explain this :-

1. The C-Cl bond in case of chlorobenzene is having some double bond like character , which is indicated by its shorter bond length. thus it indicates the back-flow of electrons from the Chlorine to the Carbon. Thus the polarity decreases and it shows non polar character.

2. The Carbon atom shows different electronegativities on the basis of its hybridisation. The electronegativities follow the following sequence:-

sp > Sp² > sp³

As in this case we have the chlorobenzene which is having Sp² hybrid carbon that is more electronegative than sp³ hybrid carbon atom in cyclohexyl chloride. and due to this the carbon of chlorobenzene has a good hold on the electron and so it shows non polar behaviour in case of chlorobenzene.