See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Solution: Turning Plane Polarised Light **Understanding the Property:** The ability of a compound to rotate the plane of polarisation of polarised light is called **optical activity**. **Why Option (3) is Correct:** 1. **Definition of Optical Activity**: Optically active compounds contain chiral centers (asymmetric carbon atoms) that interact asymmetrically with polarised light, causing rotation of the plane of polarisation. 2. **Distinguishing from other options**: - **(1) Photolysis**: Decomposition by light—unrelated to polarisation - **(2) Phosphorescence**: Emission of light after excitation—a luminescence phenomenon - **(4) Polarization**: General term for creating polarised light, not the property of rotating it 3. **Key characteristic of optically active compounds**: - Molecules with chiral centers (like $D$-glucose, $L$-amino acids) rotate plane-polarised light either **clockwise (dextrorotatory, +)** or **counterclockwise (levorotatory, −)** **Answer: (3) Optical activity** — This is the specific property describing a compound's ability to rotate the plane of polarised light.