Which combination lists all three types of isomers described?

• A. Structural, Optical, Geometric
• B. Structural, Optical, Cis-trans
• C. Structural, Optical, Enantiomer
• D. Optical, Cis-trans, Geometric

Answer: (B)

The key idea is recognizing the three main categories of isomers relevant in biology: structural (constitutional) isomers, optical isomers, and geometric (cis-trans) isomers. Structural isomers differ in how atoms are connected. Optical isomers are non-superimposable mirror images, known as enantiomers, a type of isomerism tied to chirality. Geometric or cis-trans isomerism arises from restricted rotation around a double bond or in a ring, giving two distinct spatial arrangements.

The best choice lists all three categories explicitly: Structural, Optical, and Cis-trans. This covers connectivity differences, mirror-image forms, and the distinct cis/trans arrangements. Calling one of these categories “Enantiomer” would misrepresent enantiomers as a separate category, since an enantiomer is a type of optical isomer. And a option that omits structural isomerism fails to capture all three forms.