In the reaction sequence, $\left[\mathrm{X}\right]$ is ketone;

$\left[\mathrm{X}\right]$ will be :-

In the given reaction : 

$\left(\mathrm{A}\right)$ and $\left(\mathrm{B}\right)$ are:

The conversion:

can be effected by using the reagent

Which of the following hydrogens will be the most acidic?