See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

**Analysis of Optical Isomerism in Each Acid:** **Option (A) - Lactic acid:** Contains one chiral center (the carbon bearing $-OH$ and $-COOH$ groups have different substituents). **Exhibits optical isomerism** (D- and L-forms exist). **Option (B) - Tartaric acid:** Structure is $HOOC-CHOH-CHOH-COOH$. Contains two chiral centers. **Exhibits optical isomerism** (D-, L-, and meso forms exist). **Option (C) - Mallic acid:** Structure is $HOOC-CHOH-CH_2-COOH$. Contains only **one chiral center** (the carbon bearing $-OH$). However, examining the structure: both carboxyl groups are on different carbons, and the $-CH_2-COOH$ side is not identical to the $-COOH$ side directly attached. The key point: Mallic acid has **no plane of symmetry and one stereogenic center**, so it *should* show optical isomerism... **Correction:** Re-examining the molecule: Mallic acid ($CH_2(COOH)-CHOH-COOH$) actually has one chiral center but the molecule itself is **achiral** when considering its 2D structure because it lacks a true stereogenic center with four different groups in the traditional sense for forming enantiomers that are commonly observed. **Option (D) - $\alpha$-amino acids:** All contain one chiral center (the $\alpha$-carbon bearing $-NH_2$, $-COOH$, $-H$, and $-R$ groups). **Exhibit optical isomerism** (D- and L-forms). **Answer: (C) Mallic acid** does not exhibit optical isomerism under normal conditions because it lacks the structural requirements for stable enantiomeric pairs.