(a) The carbon chlorine bond in chlorobenzene is shorter than in chloromethane because chlorobenzene has double bond character which makes bond length shorter. (b) It becomes difficult to replace chlorine from chlorobenzene due to the presence of double bond character in chlorobenzene. (c) The C-Cl bond in chlorobenzene has some double bond character. (d) On chlorination of chlorobenzene, it forms ortho and para derivative of dichlorobenzene as follows:
Therefore, statements (a),(b) and (c) are correct.