In chemistry, stereo isomerism is best described as what?

• A. Different connectivity of atoms
• B. Same structure but different spatial arrangement in 3D
• C. Change in oxidation state
• D. Rotation around a single bond

Answer: (B)

Stereoisomerism arises when molecules have the same connectivity and the same molecular formula, but their atoms are arranged differently in three-dimensional space. This means the bonds are the same, but the spatial orientation of those atoms differs, leading to distinct isomers such as mirror-image enantiomers or non-mirror diastereomers. Rotation around a single bond can freely interconvert different shapes, so those forms are conformers rather than separate stereoisomers. Oxidation state changes are a different kind of transformation and do not define stereoisomerism. Therefore, the idea described as having the same structure but a different 3D arrangement best captures stereoisomerism.