Dehydration of which of the following compounds gives only $hept-3-ene$?

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

$CH_3MgBr + \text{Cyclopentanone}$ $\xrightarrow{H_3O^{+}} A$ $\xrightarrow{HBr} B$ $\xrightarrow{Mg/\text{ether}} C$ $\xrightarrow{HCHO}_{H_3O^{+}} D$ $\xrightarrow{HI} E$
$E$ is

Give the structures of $A$,$B$,and $C$ in the following reaction:
$CH_3-CH_2-CH(OH)-CH_3$ $\xrightarrow{Cu, 520 \ K} (A)$ $\xrightarrow{C_2H_5MgBr} (B)$ $\xrightarrow{H_3O^+} (C)$

$CH_3-CH_2-CH=CH_2$ $\xrightarrow[CCl_4]{HCl} X$ $\xrightarrow{Aq. NaOH} Y$ $\xrightarrow[\Delta]{Conc. H_3PO_4} Z$
The major product $Z$ is:

$A$ sample of $4.5 \ g$ of an unknown monohydric alcohol,$ROH$,was added to methylmagnesium iodide. $A$ gas is evolved,collected,and its volume is measured to be $3.1 \ L$ at $NTP$. The molecular weight of the unknown alcohol is $g/mol$. [Nearest integer]