See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Optical Activity Analysis **Optical activity** requires a molecule to have a chiral center (asymmetric carbon with four different groups). ## Analyzing each compound: **(1) $CH_2Cl_2$** — The central carbon has two identical Cl atoms. Not chiral. **Optically inactive.** **(2) $CHCl_3$** — The central carbon has three identical Cl atoms. Not chiral. **Optically inactive.** **(3) Meso form of tartaric acid** — Although tartaric acid has chiral centers ($-CHOH-CHOH-$), the meso form has internal symmetry (mirror plane). The optical rotations of the two chiral centers cancel. **Optically inactive.** **(4) Glyceraldehyde** — Structure: $CHO-CHOH-CH_2OH$ - The middle carbon ($CHOH$) has **four different groups**: $-CHO$, $-OH$, $-H$, $-CH_2OH$ - This is a genuine chiral center with no plane of symmetry. **Optically active.** ## Answer: **(4) Glyceraldehyde** is optically active because it contains an asymmetric carbon atom with four distinct substituents, allowing it to rotate plane-polarized light.