See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

**Step 1: Identify the structure of butane-2,3-diol** Butane-2,3-diol has the structure: $CH_3-CHOH-CHOH-CH_3$ The two hydroxyl groups are on carbons 2 and 3 (adjacent carbons). **Step 2: Identify stereogenic centers** Both C2 and C3 are stereogenic centers since each has four different groups attached: - C2: $CH_3$, $OH$, $H$, $-CHOH-CH_3$ - C3: $CH_3$, $OH$, $H$, $-CHOH-CH_3$ **Step 3: Determine possible stereoisomers** With 2 stereogenic centers, maximum possible stereoisomers = $2^2 = 4$ These are: $(2R,3R)$, $(2S,3S)$, $(2R,3S)$, and $(2S,3R)$ **Step 4: Check for meso compound** The $(2R,3S)$ and $(2S,3R)$ forms are enantiomers of each other. However, due to the symmetry of the molecule, $(2R,3S)$ is a **meso compound** (optically inactive despite having stereogenic centers). **Step 5: Count optically active stereoisomers** Optically active stereoisomers: - $(2R,3R)$ — optically active - $(2S,3S)$ — optically active (enantiomer of above) - $(2R,3S)$ — meso (optically inactive) ✗ **Number of optically active stereoisomers = 2** **Answer: (B) 2**