Which of the following are used to convert $\mathrm{RCHO}$ into${\mathrm{RCH}}_2\mathrm{OH}$?

In the following reaction sequence: 

Compound $\mathrm{I}$ is

 the reactant $\mathrm{A}$ is:

cannot be prepared by:

Consider the following sequence of reactions.

 $\mathrm{Z}\stackrel{{\mathrm{PCl}}_5}{\to }\mathrm{X}\stackrel{\mathrm{Alc}.\mathrm{KOH}}{\to }\mathrm{Y}\underset{2{\mathrm{H}}_2\mathrm{O}/\mathrm{\Delta }}{\overset{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}\mathrm{Z}$

$\text{'}\mathrm{Z}\text{'}$ is

The product $\left(\mathrm{R}\right)$ of the following reaction sequence is

The aldehydes which will not form Grignard product with one equivalent of Grignard reagents are
$\left(\mathrm{A}\right)$

$\left(\mathrm{B}\right)$

$\left(\mathrm{C}\right)$

$\left(\mathrm{D}\right)$

Write the structures of the main products in the following reactions: