Which of the following undergoes nucleophilic substitution exclusively by $S_N1$ mechanism?

$C_6H_6 + CH_3CH_2CH_2Cl + AlCl_3 \to X$ (Major product)
$X$ (Major product) $\xrightarrow{HNO_3 + H_2SO_4} Y$ (Major product) $\xrightarrow{Sn + HCl} Z$ $\xrightarrow{H_2SO_4 + SO_3} W$
$W$ is

The dehydrobromination of $2$-bromobutane results in the formation of which of the following?

Which one of the following is more readily hydrolysed by $S_{N}1$ mechanism?

Arrange the following compounds in order of decreasing rate of hydrolysis for $S_{N}1$ reaction:
$(I) \ C_6H_5-CH_2-Br$
$(II) \ p-CH_3-C_6H_4-CH_2-Br$
$(III) \ p-CH_3CH_2-C_6H_4-CH_2-Br$
$(IV) \ p-(CH_3)_2CH-C_6H_4-CH_2-Br$

Select the correct decreasing order of boiling points of compounds from the following.