The lowest energy conformer of $n$-butane is

With respect to the conformers of ethane,which of the following statements is true?

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

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

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:

Statement $I$: Staggered conformation of ethane is more stable than the eclipsed conformation.
Statement $II$: The torsional strain in staggered conformation is more than in the eclipsed conformation.