Staggered and eclipsed conformers of ethane are:

We start by recalling the basic idea of conformational isomerism. In a single-bonded molecule such as ethane, the two carbon atoms are joined by a $$\mathrm{C{-}C}$$ sigma bond. Rotation about this sigma bond is possible because a sigma bond is cylindrically symmetrical. As we rotate one $$\mathrm{CH_3}$$ group with respect to the other through an angle $$\theta$$, different spatial arrangements of the atoms are obtained without breaking any bond.

Among the infinitely many possible values of $$\theta$$ (from $$0^{\circ}$$ to $$360^{\circ}$$), two extreme positions are especially important:

• When $$\theta = 0^{\circ}$$, the hydrogen atoms on one carbon are directly in front of those on the other carbon. This arrangement is called the eclipsed conformer.

• When $$\theta = 60^{\circ}$$, each hydrogen on the front carbon lies exactly between two hydrogens on the rear carbon. This arrangement is called the staggered conformer.

These different arrangements are produced solely by rotation around the single bond; no bonds are broken or re-formed. Therefore, the staggered and eclipsed forms are not different compounds in the usual sense—they are simply different conformations (also known as conformers) of the same molecule.

In nomenclature, species that differ only by rotation about a single bond are called rotational isomers or, more concisely, rotamers. The word itself comes from “rotation” + “isomer.”

Let us verify that none of the other listed terms apply:

• Polymers are very large molecules made by linking together many repeating units (monomers). The staggered and eclipsed forms of ethane are not larger chains; they are simply two positions of the same small molecule. Hence, “polymers” is not appropriate.

• Enantiomers are non-superimposable mirror-image stereoisomers that arise from chirality. Ethane in any conformation is achiral, so these two conformers cannot be enantiomers.

• Mirror images would again imply a relationship of chirality between two molecules, which is absent here.

Therefore, the only correct descriptive term for the relationship between the staggered and eclipsed conformers of ethane is “rotamers.”

Hence, the correct answer is Option B.