Answer: I- > Br- > Cl- > F-.
- A F- > Cl- > Br- > I-
- B OH- > F- > Cl- > Br-
- C Br- > I- > Cl- > F-
- D I- > Br- > Cl- > F-
Correct answer: D. I- > Br- > Cl- > F-
Explanation: Leaving group ability correlates with the stability of the leaving group anion (its ability to accommodate the negative charge). Larger halogens are more polarisable and stabilise the anion better: I⁻ > Br⁻ > Cl⁻ > F⁻.
SN2 proceeds in a single step with backside attack and inversion of configuration, while SN1 forms a planar carbocation intermediate first, leading to racemisation.
Concept context
Study carbon-halogen compounds: how they are made, how they react via SN1/SN2 and elimination, their stereochemistry, and their environmental impact.