Arrange the following halides in the decreasing order of their reactivity towards $S_{N^1}$ reaction.
$(I) \ CH_3CH_2CH_2Cl$ $(II) \ CH_2 = CH - CH(Cl)CH_3$
$(III) \ CH_3CH_2CH(Cl)CH_3$

Identify the product $B$ in the following reaction sequence:
$1$-bromo-$4$-chlorobenzene $\xrightarrow[\text{Dry ether}]{Mg (1 \text{ equivalent})} (A)$ $\xrightarrow{HO-CH_2-CH_2-Cl} (B)$

Which of the following halides undergoes hydrolysis most rapidly?

The $S_N2$ product of the following reaction is:

Benzyl bromide on reaction with magnesium in the presence of dry ether gives $'X'$. $'X'$ on reaction with ethanol gives $'Y'$. Then the compound $Y$ is

Consider the reaction sequence shown below:
$Br-CH_2-CHO$ $\xrightarrow[\text{dry } HCl \text{ gas}]{\text{EtOH (excess)}} A$ $\xrightarrow{^tBuO^-K^+} B$
[Where $Et \Rightarrow -C_2H_5$,$^tBu \Rightarrow (CH_3)_3C^-$]
Identify the major products $A$ and $B$ formed respectively.