Optical isomers share identical atomic composition

Steps:

• Identify optical isomers as enantiomers: non-superimposable mirror images of each other.
• Recognize they have the same atoms bonded in the same order, differing only in 3D arrangement.
• Recall empirical formula as the simplest whole-number ratio of elements present.
• Conclude this ratio is unchanged by spatial configuration, making it identical for the pair.

Why A is correct:

• Optical isomers are stereoisomers with the same molecular formula by definition, so their empirical formula—the reduced ratio of atoms—is exactly the same.

Why the others are wrong:

• B: Functional groups depend on connectivity, which is identical, but empirical formula specifically addresses composition, not group types.
• C: Structural formula shows atom connections, which match, but it excludes the spatial difference defining optical isomerism.
• D: Not enough information.

Final answer: A