Conformational isomerism occurs when a molecule can adopt different spatial arrangements due to rotation around a single bond. Among the given options, only CH4 exhibits conformational isomerism.

Explanation:
- Conformational isomerism arises due to the ability of a molecule to rotate around a single bond without breaking it. The different arrangements of atoms resulting from this rotation are called conformers or conformations.
- In the case of CH4, it is a tetrahedral molecule with four hydrogen atoms bonded to a central carbon atom. The carbon-hydrogen bonds can rotate freely without breaking, allowing for different spatial arrangements of the hydrogen atoms.
- The rotation can occur around any of the carbon-hydrogen bonds, resulting in different conformations. The different conformations are represented by Newman projections, which show the molecule viewed along the carbon-hydrogen bond axis.
- For example, CH4 can adopt different conformations where the hydrogen atoms are positioned at different angles relative to each other. These conformations are called staggered and eclipsed conformations.
- In the staggered conformation, the hydrogen atoms are positioned as far apart as possible, resulting in lower steric hindrance and more stable conformation. This conformation is energetically favored.
- In the eclipsed conformation, the hydrogen atoms are positioned directly opposite each other, resulting in higher steric hindrance and less stable conformation. This conformation is energetically disfavored.
- The ability of CH4 to freely rotate around its carbon-hydrogen bonds allows it to interconvert between different conformations, resulting in conformational isomerism.

In conclusion, CH4 is the only molecule among the given options that exhibits conformational isomerism due to the rotation of its carbon-hydrogen bonds.