See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Solution **Understanding the Key Concept:** A molecule that is superimposable on its mirror image is **achiral** (optically inactive), even if it contains asymmetric carbon atoms. This occurs when internal symmetry cancels out chirality. **Why Option (1) - Meso Compound is Correct:** A **meso compound** is defined as: - Contains one or more asymmetric (chiral) carbon atoms - Possesses an internal plane of symmetry - Is superimposable on its mirror image - Shows no optical activity despite having stereocenters **Example:** Tartaric acid with 2 chiral centers $$\text{HOOC-CH(OH)-CH(OH)-COOH}$$ The two chiral centers have opposite configurations (D and L), creating a plane of symmetry through the middle. Therefore, the molecule is achiral overall. **Why Other Options are Wrong:** - **(2) Erythro isomer:** Specific stereoisomer designation; not necessarily superimposable on mirror image - **(3) Threo isomer:** Similar to erythro; describes relative stereochemistry, not achirality - **(4) Glycol:** A functional group (diol); not defined by chirality properties **Answer: (1) A meso compound** — This is the only classification that explicitly describes molecules with asymmetric carbons yet superimposable on their mirror images.