When concentrated $H_2SO_4$ reacts with $X$ at a temperature of $160 - 170 \, ^\circ C$,ethylene is obtained. What is $X$?

Of the following alcohols,the one that would react fastest with conc. $HCl$ and anhydrous $ZnCl_{2}$ is,

Identify the correct trend of acidic strength for the given alcohols.

When a Grignard reagent reacts with $(B)$,product $(D)$ is obtained. Reactant $(A)$ of the above reaction is:
$(A)$ $\xrightarrow{PBr_3} (C)$ $\xrightarrow{Mg, \text{ether}} \text{Grignard reagent}$
$(A) \xrightarrow{Na_2Cr_2O_7, H_2SO_4} (B)$
$\text{Grignard reagent} + (B) \to (D) \xrightarrow{H_3O^\oplus} (3,4-\text{dimethylhexan-3-ol})$

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

$4$-chloro-butan-$1$-ol $+ NaOH \to (B)$. The product $(B)$ of the above reaction is: