Which of the following alkyl halides is most reactive towards substitution by the $S_{N}1$ mechanism?

The reaction of $1$-bromohexane with aqueous $NaOH$ solution follows the order

Among the following organic halides,arrange them in the increasing order of their dehydrohalogenation reactions in the presence of alcoholic $KOH$:
$(A)$ $CH_3-CH_2-Br$
$(B)$ $CH_3-CH_2-CH_2-Br$
$(C)$ $CH_3-CH(Br)-CH_3$
$(D)$ $(CH_3)_3-CBr$

Identify the major product formed when propene is treated with hydrogen chloride followed by Swarts reaction.

Match the following:

Column $I$	Column $II$
$A$. $CH_3-CHBr-CD_3$ on treatment with alc. $KOH$ gives $CH_2=CH-CD_3$ as a major product.	$P$. $E1$ reaction
$B$. $Ph-CHBr-CH_3$ reacts faster than $Ph-CHBr-CD_3$.	$Q$. $E2$ reaction
$C$. $Ph-CH_2-CH_2Br$ on treatment with $C_2H_5OD / C_2H_5O^-$ gives $Ph-CD=CH_2$ as the major product.	$R$. $E1cb$ reaction
$D$. $PhCH_2CH_2Br$ and $PhCD_2CH_2Br$ react with same rate.	$S$. First order reaction

The compound which undergoes $S_{N^1}$ reaction most rapidly is