Which of the following is an example of $S_N2$ reaction?

The reaction of $p-$bromobenzyl chloride with $NaCN$ in ethanol gives:

Identify the correct order for the given property for the following compounds. Choose the correct answer from the options given below:
$(A)$ Boiling Point: $CH_3CH_2Cl < CH_3CH_2CH_2Cl < CH_3CH_2CH_2CH_2Cl$
$(B)$ Density: $CH_3CH_2Br < CH_3CH_2Cl < CH_3CH_2I$
$(C)$ Boiling Point: $CH_3CH_2Br < (CH_3)_2CHBr < (CH_3)_3CBr$
$(D)$ Density: $CH_3CH(I)Br < CH_3CH_2CH_2Br < CH_3CH(Br)Cl$
$(E)$ Boiling Point: $CH_3CH_2CH_2CH_2Cl > (CH_3)_2CHCH_2Cl > (CH_3)_3CCl$

For $(i) \, I^{-}, \, (ii) \, Cl^{-}, \, (iii) \, Br^{-}$,the increasing order of nucleophilicity would be

Two bottles containing $C_6H_5I$ and $C_6H_5CH_2I$ have lost their original labels. They are labeled as $A$ and $B$ for testing. $A$ and $B$ are taken separately in test tubes and boiled with $NaOH$ solution. The final solution of each test tube is acidified with dilute $HNO_3$ and a little $AgNO_3$ is added. Solution $B$ gives a yellow precipitate. Which of the following statements is correct?

$A$ solution of $(\pm)-2$-chloro-$2$-phenylethane in toluene is mixed slowly with a small amount of $SbCl_5$. The reaction proceeds due to the formation of: