Which of the following is most reactive towards nucleophilic substitution reaction?

Which of the following compounds undergoes nucleophilic substitution reaction most easily via the $S_{N}1$ mechanism?

$CH_3-CH_2-CH_2-Cl$ $\xrightarrow{KOH_{(aq)}} X$ $\xrightarrow{H^{+}/\Delta} Y$ $\xrightarrow{Cl_2/H_2O} Z$ (Major); $Z$ is

Major product of the reaction is :

An 'Assertion' $(A)$ and a 'Reason' $(R)$ are given below. Choose the correct answer from the following options.
Assertion $(A)$: Vinyl halides do not undergo nucleophilic substitution easily.
Reason $(R)$: Even though the intermediate carbocation is stabilized by loosely held $p-$ electrons,the cleavage is difficult because of strong bonding.

Which describes the best stereochemical aspects of the following reaction?
$Ph-C(CH_3)(CD_3)(OH) + HBr \rightarrow \text{Product}$