Geometrical isomerism due to restricted rotation around double bonds

Steps:

• Identify the molecular structure: Assume it features a carbon-carbon double bond with different substituents on each carbon.
• Check for cis-trans configuration: Verify if substituents are on the same side (cis) or opposite sides (trans).
• Confirm no free rotation: Double bonds prevent rotation, allowing distinct spatial arrangements.
• Rule out other types: No chiral centers or chain/position variations present.

Why B is correct:

• Geometrical isomerism occurs in compounds with double bonds or rings where substituents have cis/trans arrangements, as per the definition of stereoisomerism without free rotation.

Why the others are wrong:

• A: Chain isomerism involves different carbon skeletons, not spatial arrangements.
• C: Optical isomerism requires chiral centers with non-superimposable mirror images.
• D: Positional isomerism features functional groups at different positions on the same skeleton.

Not enough information: No structure provided to confirm.

Final answer: B