Which of the structures $(a - d)$ will be produced if a "ring flip" occurs in the following compound in chair form?

Given below are two statements:
Statement $I$: There are several conformers for $n$-butane. Out of those conformers,the fully eclipsed conformer (dihedral angle $0^{\circ}$) is the least stable and the anti-staggered conformer (dihedral angle $180^{\circ}$) is the most stable.
Statement $II$: As the dihedral angle increases from $0^{\circ}$ to $60^{\circ}$,torsional strain decreases from the fully eclipsed conformer $(X)$ to the gauche conformer $(Y)$.
In the light of the above statements,choose the correct answer from the options given below:

Which is the most stable conformation of ethylene glycol?

The most stable conformation of $2,3-$dibromobutane is

$HO-CH_2-CH_2-F$
Which conformer of the above compound is most stable across the $C-C$ bond?

Arrange the given compounds in decreasing order of their potential energy: