Which of the following represents the sawhorse projection of the staggered conformation of 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:

On another planet,the gauche and anti forms of $1, 2-$dichloroethane freeze and single bond rotation stops. Under these conditions,these two forms can be considered as:

What do you mean by dihedral angle or torsional angle?

The total number$(s)$ of stable conformers with non-zero dipole moment for the following compound is (are):

The isomers which can be converted into another forms by rotation of the molecules around single bond are