AIIMS 2019 Chemistry Nucleophilic Substitution Reactions MCQ Question

In an Sₙ2 reaction, the nucleophile attacks the electrophile in a single concerted step, favoring less sterically hindered substrates. Carbocation stability decreases with increasing steric hindrance, making option D (iii > i > ii) correct, as the least hindered substrate (iii) reacts more readily than the more hindered ones (i and ii). Options A, B, and C incorrectly rank the substrates based on steric hindrance, failing to recognize that greater steric bulk around the electrophilic carbon impedes the nucleophilic attack, thus slowing the reaction rate.