Replacement of 'Cl' of chlorobenzene to give phenol requires drastic conditions but chlorine of 2,4-dinitrochloro benzene is readily replaced because
1. NO₂ makes the ring electrons rich at ortho and para position
2. NO₂ withdraws electrons from meta position
3. NO₂ donates electrons at m-position
4. NO₂ withdraws electrons from ortho and para positions