Which of the following S _ N 2 reactions will proceed at the fastest rate under identical conditions?

Step-by-step solution

The given reactions are S_ N 2 substitutions where different nucleophiles attack butyl methanesulfonate. The solvent used is ethanol, which is a polar protic solvent. In polar protic solvents, smaller anions are heavily solvated due to strong hydrogen bonding, which decreases their nucleophilicity. The order of nucleophilicity for halide ions in polar protic solvents is I⁻ > Br⁻ > Cl⁻ > F⁻ . Neutral molecules like ethanol ( CH₃CH₂OH ) are weaker nucleophiles compared to anionic nucleophiles like I⁻ . Therefore, I⁻