Tertiary alkyl halide is practically to substitution by ( S_ N 2 ) mechanism because of

Step-by-step solution

In ( S_ N 2 ) reactions, nucleophile approach to the carbon bearing the leaving group, the presence of bulky substituents inhibits the incoming nucleophile which decrease the rate of reaction, therefore, alkyl halides having bulkier substituents or higher degree alkyl halides preferably react through ( S N₁ ) path. The order of reactivity for ( S_ N 1 ) path is ( 1^ >2^ >3 )