Which of the following plots are correct for potential energy of butane as function about ${\mathrm{C}}_2-{\mathrm{C}}_3$ bond?

When the dihedral angle = 0° or 360°, (syn confirmation) in butane, the two methyl groups are in close proximity with the molecule, therefore the In the anti conformation (when the dihedral angle = 180°) the potential energy is at its lowest,

Physical energy due to its nature of transformation is known as "potential energy". The Potential energy of n-butane is minimum for unsteady conformations because of no steric resistance. The potential potency of n-butane is very high in the complete concordance due to the divergence of the active group.

Hence the correct option is (a),(b).