Cyclohexyl chloride is more reactive towards nucleophilic substitution reaction because C—Cl bond strength is less in cyclohexyl chloride than chlorobenzene. In cyclohexyl chloride chlorine atom is bonded to sp3 hybrid carbon atom while in chlorobenzene chlorine is bonded to sp2 hybrid carbon atom that's why C—Cl bond is more strong in chlorobenzene and less reactive toward Nucleophilic substitution.
