Which of the following reactions is used for the conversion of alkyl chloride to alkyl iodide?

An alkyl bromide $(A)$ forms a Grignard reagent which on treatment with water yields $n$-hexane. When $(A)$ is treated with sodium in dry ether,$4,5$-diethyloctane is formed. The structure of $(A)$ is:

$1,2-dichlorocyclopentane$ $\xrightarrow{1 \text{ equivalent } Mg, \text{ ether}} X$ $\xrightarrow{D_2O} Y;$
$Y$ is:

The most stable product of the following reaction is:

What is the order of ease of dehydrohalogenation of alkyl halides?

The major product obtained in the above reaction is