Which of the following reactions is expected to take place by the $S_N2$ mechanism?

What is the product formed by the monochlorination of ethylbenzene with $Cl_2$ in the presence of heat?

Bottles containing $C_6H_5I$ and $C_6H_5CH_2I$ lost their original labels. They were labelled $A$ and $B$ for testing. $A$ and $B$ were separately taken in test tubes and boiled with $NaOH$ solution. The end solution in each tube was made acidic with dilute $HNO_3$ and then some $AgNO_3$ solution was added. Substance $B$ gave a yellow precipitate. Which one of the following statements is true for this experiment?

The major product $(A)$ is:

In a $S_N2$ substitution reaction of the type $R-Br + Cl^- \xrightarrow{DMF} R-Cl + Br^-$,which one of the following has the highest relative rate?

Addition of $KI$ accelerates the hydrolysis of primary alkyl halides because