Consider the S_ N 2 reaction of ethyl bromide with the following substituted phenoxide ions: (I) p -methoxyphenoxide (II) p -nitrophenoxide (III) phenoxide (IV) p -methylphenoxide The correct decreasing order of the rate of reaction is:

Step-by-step solution

The rate of an S_ N 2 reaction depends on the nucleophilicity of the attacking species. For substituted phenoxides, electron-donating groups increase the electron density on the oxygen atom, thereby increasing its nucleophilicity. Conversely, electron-withdrawing groups decrease the electron density and reduce nucleophilicity. The methoxy group ( -OCH₃ ) exerts a strong +R effect, significantly increasing electron density. The methyl group ( -CH₃ ) exerts a weaker +I and hyperconjugation effect. The nitro group ( -