Chemistry - Halogen Derivative Question with Solution | TestHub

A polar protic solvent can participate in hydrogen bonding with a nucleophile. This make the nucleophile less reactive, as its lone pair becomes less available to attack.
The ability of nucleophiles to participate in hydrogen bonding decreases as we go down the periodic table. This means that the lone pairs of iodide ion will be considerably more “free” than those of fluoride, resulting in higher rates (and greater nucleophilicity).