Give reasons:
(i). `C-Cl` bond length in chlorobenzene is shorter than `C-Cl` bond length in `CH_(3)-Cl`
(ii). The dipole moment of chlorobenzene is less than of cyclohexyl chloride.
(c). `S_(N^(1))` reactions are are accompanied by racemisation is optically active alkyl halides.

Explanation

Chlorobenzene can be regarded as a resonance hybrid of five structure. As a result C-Cl bond in chlorobenzene has some double bond character and hence shorter (169 pm) than C-Cl bond in `CH_(3)-Cl` (177 pm) which has pure single bond character.
Alternately, in `CH_(3)-Cl,Cl` is attached to a `sp^(3)`-hybridized carbon while in chlorobenzene it is attached to a `sp^(2)`-hybridized carbon. since a `sp^(2)`-hybridized orbital is smaller in size as compared to a `sp^(3)`-hybridized
ltBrgt orbital of carbon, therefore, `C_Cl` bond in chlorobenzene is shorter (169 pm) than C-Cl bond length in `CH_(3)-Cl` (177 pm).