Question: is i or f a better nucleophile?
Answer: I⁻ is a better nucleophile than F⁻ in polar protic solvents. F⁻ is a better nucleophile than Br⁻ in polar aprotic solvents. ... This creates a "shell" of solvent molecules around the nucleophile. The nucleophile has to push this shell of solvent molecules out of the way to attack the carbon bearing the leaving group.