Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile,`E^+`.
Chlorobenzene,2,4- dinitrochlorobenzene, p-nitrochlorobenzene

Explanation

Electron density of the benzene nucleus increases in presence of electron-donating group (activating group). Consequently, electrophiles can easily attack the benzene nucleus. On the other hand, electron density of the benzene nucleus decreases in presence of electron-withdrawing group (deactivating group). This makes electrophillic substituation difficult for the benzene nucleus.
Therefore, order of the different compounds according to their decreasing relative reactivity with an electrophile `E^(+)` is-
Chlorobenzne `gt` p-nitrochlorobenzne `gt` 2, 4-dinitrochlorobenzene