The following tertiary alkyl bromides undergo anreaction in aqueous acetone to form the corresponding tertiary alcohols. Rank the alkyl bromides from most reactive to least reactive.

Strongly activating substituents donate electron to the ring by resonance because of the lone pair present and there by increases the reactivity towards electrophilic substitution reaction. Deactivating substituents withdraw electrons from the ring.

Substituents present on a benzene ring can determine its reactivity towards electrophilic substitution reaction. Electron donating substituents will stabilize the tertiary carbocation by donating electrons. This in turn increase the formation of carbocation easily.Electron donating groups destabilize the carbocation by withdrawing electrons from the ring.Here compound B is most reactive because of ethoxy group present in para position. Then comes D and A. Compound E and C containing deactivating substituents in which, is the strong deactivating substituent give its low reactivity compared to other compounds.

Thus, the decreasing order of reactivity can be show as below

Decreasing order of reactivity