Question

# The conformations of n-butane, commonly known as eclipsed, gauche and anti conformations can be interconverted by :a.) Rotation around $C - H$ bond of a methyl groupb.) Rotation around $C - H$ bond of a methylene groupc.) Rotation around $C1 - C2$ linkaged.) Rotation around $C2 - C3$ linkage

Hint : The conformations of butane can be interconverted only by rotation around the central carbon atoms in butane.

The three conformations of butane given in question i.e. eclipsed, anti and gauche can be interconverted by rotation around $C2 - C3$ linkage.