AIIMS 2018 Chemistry Nucleophilic Substitution Reactions MCQ Question

In an Sₙ2 reaction, the rate of nucleophilic substitution is influenced by the steric hindrance and the nature of the leaving group. Option B (II > I > III > IV) is correct because it ranks the substrates based on their accessibility to the nucleophile; primary substrates (II) react faster than secondary (I), which in turn react faster than tertiary (III) and quaternary (IV) substrates due to increased steric hindrance. Other options are incorrect as they misrepresent the reactivity order by placing more hindered substrates before less hindered ones, which contradicts the fundamental principles of Sₙ2 mechanisms.