Aliphatic nucelophilic substitution is mainly placed by two mechanisms (i.e.,) $S_{N^1}\&S_{N^2}.$   Primary halides are mainly undergone by $S_{N^2}$  mechanism and are favorable in polar aprotic solvents. $S_{N^1}$   reactions takes place mainly by tertiary halides and are more favorable in polar protic solvents. In the case of tertiary halides, ${\mathrm{E}}_1$   Comes competition to  $S_{N^1}$  reaction. Keeping in view of these general points, answer the following questions.