Towards, nucleophilic substitution chlorobenzene is
 

• A functional group within another molecule that lacks electrons is replaced by an electron-rich chemical species in a chemical reaction known as a nucleophilic substitution.
• The lone pairs on the Cl atom in chlorobenzene engage in resonance with the pi electrons of benzene, giving the C-Cl bond double bond characteristics, which reduces reactivity.

Hence , the correct option  (D). Less reactive than benzyl chloride