SN2 Hydrolysis Rate in Primary Haloalkanes

Steps:

• Identify mechanism: Primary haloalkanes undergo SN2 hydrolysis, rate = k[alkyl halide][nucleophile].
• Compare nucleophiles: H2O (A) is weak; OH⁻ (B–D) is strong, so B–D faster than A.
• Assess leaving groups: Br⁻ (B) leaves easier than Cl⁻ (C, D) due to weaker C–Br bond.
• Consider chain length: Minimal steric effect in primaries, but C2 (B) slightly faster than C3 (C) or C4 (D).

Why B is correct:

• B uses strong nucleophile OH⁻ and best leaving group Br⁻ among options, maximizing SN2 rate per bond strength trend (C–I > C–Br > C–Cl).

Why the others are wrong:

• A: Weak nucleophile H2O leads to slow neutral hydrolysis.
• C: Cl⁻ poorer leaving group than Br⁻ slows rate despite OH⁻.
• D: Cl⁻ and longer chain slightly increase steric hindrance, slowing more than C.

Final answer: B