Which of the following substances will produce acetaldehyde in the presence of an aqueous solution?

The alcohol which reacts most easily with conc. $HCl$ is

Consider the following reactions:
$X + HCl \xrightarrow{\text{Anhydrous } AlCl_3} C_2H_5Cl$
$Y \xrightarrow{\text{Anhydrous } ZnCl_2 / HCl} C_2H_5Cl$
$Y$ can be converted to $X$ on heating with which of the following reagents?

Glycerol has strong intermolecular hydrogen bonding; therefore,it is:

What will be $A$,$B$,$C$,and $D$ in the following reaction sequence?
Cyclohexanol $\xrightarrow[H_2SO_4]{CrO_3} A$ $\xrightarrow[(ii) H_3O^+]{(i) CH_3MgI} B$ $\xrightarrow{\Delta, H_2SO_4} C$ $\xrightarrow[(ii) H_2O_2, NaOH]{(i) (BH_3)_2} D$

What is the first step in the dehydration of alcohol to form an alkene by heating with concentrated $H_2SO_4$?