Ethyl hydrogen sulphate is obtained by the reaction of $H_2SO_4$ on

What are $X$ and $Y$ in the following reactions?

Identify the reagents $X, Y, Z$ for the following dehydration reactions of alcohols:
$CH_3-CH_2-OH \xrightarrow{X} CH_2=CH_2 + H_2O$
$CH_3-CH(OH)-CH_3 \xrightarrow{Y} CH_3-CH=CH_2 + H_2O$
$(CH_3)_3C-OH \xrightarrow{Z} (CH_3)_2C=CH_2 + H_2O$

Which of the following compounds is most reactive toward acid-catalyzed hydration?

$A$ substance $C_4H_{10}O$ yields on oxidation a compound $C_4H_8O$ which gives an oxime and a positive iodoform test. The original substance on treatment with conc. $H_2SO_4$ gives $C_4H_8$. The structure of the compound is:

Which of the following compounds gives the most stable carbonium ion during dehydration?