$CH_3-C(OH)(CH_3)-CH_3 \xrightarrow[cool]{Na_2Cr_2O_7} (P)$; Product $(P)$ in the reaction is

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

Identify $Z$ in the following reaction sequence:
$C_2H_5OH$ $\xrightarrow{PBr_3} X$ $\xrightarrow{KOH(alc.)} Y$ $\xrightarrow[(ii) H_2O, \Delta]{(i) H_2SO_4} Z$

Primary alcohols on dehydration give

An alcohol $X$ $(C_4H_{10}O)$ on dehydration gives an alkene $(C_4H_8)$ as the major product,which on bromination followed by treatment with $Y$ gives an alkyne $C_4H_6$. The alkyne $C_4H_6$ does not react with sodium metal. What are $X$ and $Y$?

Assertion : Alcohols are dehydrated to hydrocarbons in the presence of acidic zeolites.
Reason : Zeolites are porous catalysts.