Which among the following has the lowest boiling point?

The major product of the following reaction is:

An organic compound $X$ on treatment with $PCC$ in dichloromethane gives the compound $Y$. Compound $Y$ reacts with $I_{2}$ and alkali to form a yellow precipitate of triiodomethane. The compound $X$ is

Identify $Z$ in the series:
$CH_2 = CH_2$ $\xrightarrow{HBr} X$ $\xrightarrow[Hydrolysis, Na_2CO_3]{I_2 (excess)} Z$

Ethanol,when reacted with $PCl_5$,gives $A$,$POCl_3$,and $HCl$. $A$ reacts with silver nitrite $(AgNO_2)$ to form $B$ (major product) and $AgCl$. $A$ and $B$ are respectively:

The major product formed in the following reaction: $CH_3CH(Cl)CH_2CH_2OH \xrightarrow{Aq. KOH}$ is