Which of the following represents the correct order of reactivity towards an S _ N 2 reaction?

Step-by-step solution

The rate of an S_N2 reaction depends on the nature of the leaving group, the substrate structure, and the presence of substituents. Comparing the leaving groups, bromide is a better leaving group than chloride. Thus, p-cyanobenzyl bromide is more reactive than p-cyanobenzyl chloride, and p-nitrobenzyl bromide is more reactive than p-nitrobenzyl chloride. Aryl halides are highly unreactive towards S_N2 reactions due to the partial double bond character of the carbon-halogen bond and the sp^2 hybridized carbon atom.