Chemistry - Halogen Derivative Question with Solution | TestHub

$$\text{ In a }{\mathrm{S}}_{\mathrm{N}}2\text{ substitution reaction of the type }$$ $$\mathrm{R}-\mathrm{Br}+{\mathrm{Cl}}^{-}\stackrel{\mathrm{OMF}}{⟶}\mathrm{R}-\mathrm{Cl}+{\mathrm{Br}}^{-}$$ Which one of the following has the highest relative rate?NEET 2008 (Mains)