Arrange the following molecules in the correct order of stability (decreasing order):

The structures shown below represent .......

Give the difference between eclipsed ethane and staggered ethane.

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 of the following conformations of $n$-butane is the most stable?

How many eclipsed and staggered conformations of ethane are obtained during a $0^{\circ}$ to $360^{\circ}$ rotation about the $C-C$ bond?