See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: The SN2 (Substitution Nucleophilic Bimolecular) reaction proceeds through a single concerted step in which the nucleophile attacks the electrophilic carbon simultaneously as the leaving group departs. There is no intermediate; the transition state involves both the nucleophile and the electrophile (the substrate). Reasoning: Because both the nucleophile and the electrophile are involved in the single rate-determining step, the rate depends on the concentration of both species. This gives a second-order rate law overall: Rate = k[electrophile][nucleophile]. The 'bimolecular' in SN2 directly refers to this second-order kinetics involving two species in the transition state. Why other options fail: - Option (a): Rate = k[electrophile] describes a first-order process dependent only on the substrate, which is characteristic of SN1 reactions where the rate-determining step is unimolecular ionization of the substrate. - Option (c): Rate = k[nucleophile]^2 has no chemical basis for SN2; the nucleophile alone does not appear twice in the rate-determining step. - Option (d): Rate = k[electrophile]^2 also has no basis; two molecules of electrophile are not involved in the SN2 transition state. Therefore, the correct answer is B.