See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Rotation of Plane Polarised Light Measurement **Step 1: Understand optical rotation** The rotation of the plane of polarized light by optically active substances (like chiral compounds) is called optical rotation or optical activity. **Step 2: Identify the measuring instrument** A **polarimeter** is the specialized optical instrument designed specifically to measure the angle of rotation of plane-polarized light as it passes through a solution of an optically active compound. **Step 3: How a polarimeter works** - Light passes through a polarizer (creates plane-polarized light) - The polarized light passes through the sample solution - The plane of polarization rotates due to optical activity - An analyzer detects the rotation angle by comparing initial and final polarization planes **Step 4: Eliminate other options** - **(1) Manometer** — measures pressure - **(3) Viscometer** — measures viscosity/flow resistance - **(4) Refractometer** — measures refractive index **Answer: (2) Polarimeter** ✓ A polarimeter directly quantifies the optical rotation angle in degrees, making it the correct instrument for this measurement.