In a S _ N 2 substitution reaction of the type R - Br + Cl ⁻ DMF R - Cl + Br ⁻ which one of the following has the highest relative rate?

Step-by-step solution

S _ N 2 mechanism is followed in case of primary and secondary halides i.e., S _ N ² reaction is favoured by small groups on the carbon atom attached to halogens so