Which of the following compounds on oxidation gives ethyl methyl ketone?

The given reaction is known as :

Identify $Z$ in the following reaction:
$CH_3CH_2OH$ $\xrightarrow{PBr_3} X$ $\xrightarrow{alc. KOH} Y$ $\xrightarrow[{(ii) H_2O, \text{heat}}]{{(i) H_2SO_4, \text{RT}}} Z$

Compound $A$ reacts with $PCl_5$ to give $B$,which on treatment with $KCN$ followed by hydrolysis gives propionic acid. What are $A$ and $B$ respectively?

Amongst the following alcohols,which would react fastest with conc. $HCl$ and $ZnCl_2$?

Among the following compounds,which one can be dehydrated very easily?