See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Optical Isomerism: Root Cause **Step 1: Define optical isomerism** Optical isomerism occurs when molecules have the same molecular formula and connectivity but differ in their spatial arrangement, producing non-superimposable mirror images (enantiomers). **Step 2: Identify the structural requirement** For optical isomerism to exist, a molecule must contain at least one **chiral center** — a carbon atom bonded to four different groups. **Step 3: Analyze each option** - **(1) An asymmetric carbon atom** ✓ This is the chiral center required for optical isomerism. The four different groups bonded to this carbon create non-superimposable mirror images. - **(2) Centre of symmetry** ✗ The presence of a center of symmetry eliminates optical activity (the molecule becomes optically inactive). - **(3) Axis of symmetry** ✗ An axis of symmetry destroys chirality and optical activity. - **(4) Plane of symmetry** ✗ A plane of symmetry makes the molecule achiral and optically inactive. **Step 4: Conclusion** Options (2), (3), and (4) all represent **symmetry elements that eliminate optical isomerism**, not create it. Only an **asymmetric (chiral) carbon atom** is necessary and sufficient for optical isomerism. **Answer: (1) An asymmetric carbon atom**