Which of the following compounds undergoesnucleophilic substance react

1.	Which of the following compounds undergoesnucleophilic substance reaction most easily?
Answer» Solution :In `S_(n)` AR reactions, a carbanion is formed as an intermediate, so any substituent that increase the stability of carbanion and HENCE the transition STATE leading to its formation will enhance the `S_(n)` Ar reactions. To compare the rates of substitution in chlorobenzene, chlorobenzene having electron-withdrawing group, and chlorobenzene having electron-releasing group, we compare the structures carbanion (I) (from chlorobenzene). II (from chlorobenzene containing electron-withdrawing group) and III (from chlorobenzene containing electron-releasing group). (i) (ii) G-withdraws electrons, neutralises (diperses) -ve charge of the ring, stabilities carbanion, facilitates, `S_(N)` reaction (activation effect) (iii) G-releases electrons, intensifies -ve charge, destabilizes carbanion, retards `S_(N)` reaction (deactivation) `NO_(2)` is ACTIVATING group and `CH_(3) and OCH_(3)` are deactiveting group towards necluphilic aromatic substitution reactions. Hence, the correct order of nucleophilic substitution reactions