What is the relationship between the given compounds?

One of the configurations of $n$-butane is shown in the given figure. An anticlockwise rotation of $C_2$ around the $C_2-C_3$ bond by $120^\circ$ will lead to:

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:

The following eclipsed form of propane is repeated after rotation by an angle of $......^o$.

Isomerism due to rotation around the $C-C$ single bond is known as:

Which of the following isomeric structures has the lowest energy?