Which of the following is correct for the given compound?

The relation between $(X)$ and $(Y)$ is:

$A$ compound was synthesized by a student,but its structure was not identified. However,his instructor told him that it was a meso compound with $5$ carbons and $2$ stereogenic centers. Which of the following structures should the student consider as possibilities for his compound?

Which is the most stable chair form of this compound?

Consider the hydrogen atoms attached to three different carbon atoms (labeled $1$,$2$ & $3$). Rank the attached hydrogen atoms in order from most acidic to least acidic.

Which of the following exhibits geometrical isomerism?