Structural isomers differ in structure; optical isomers differ in

• A. the arrangement around a double bond
• B. mirror image relationship
• C. bond connectivity
• D. physical state at room temperature

Answer: (B)

Optical isomers are a type of stereoisomer where the same atoms and bonds are present, but the three-dimensional arrangement around a chiral center makes the molecules non-superimposable mirror images. The key feature that defines them is their mirror-image relationship: the two forms are enantiomers, each one being the exact left- or right-handed version of the other. Because of this, they rotate plane-polarized light in opposite directions and can interact differently with other chiral environments, even though they have the same connectivity and overall formula.

This is why the correct description is about mirror-image relationship. The other statements describe different ideas: arranging around a double bond refers to geometric (cis/trans) isomerism, connecting bonds refers to structural isomerism, and physical state at room temperature is not a defining feature of optical isomerism.