See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Identifying D-Threose **Step 1: Understand D-Threose Structure** D-Threose is a 4-carbon aldose (aldotetrose) with the molecular formula $C_4H_8O_4$. It has: - An aldehyde group ($CHO$) at C1 - A chiral center at C2 with $OH$ on the **right** (D-configuration) - A chiral center at C3 with $OH$ on the **left** - A primary alcohol ($CH_2OH$) at C4 **Step 2: Analyze Each Structure** | Structure | C1 | C2 | C3 | C4 | Identity | |-----------|----|----|----|----|----------| | (1) | $CHO$ | $OH$ right, $H$ left | $OH$ left, $H$ right | $CH_2OH$ | D-Erythrose | | (2) | $CHO$ | $OH$ right, $H$ left | $OH$ right, $H$ left | $CH_2OH$ | L-Threose | | (3) | $CHO$ | $OH$ left, $H$ right | $OH$ left, $H$ right | $CH_2OH$ | L-Erythrose | | (4) | $CHO$ | $OH$ left, $H$ right | $OH$ right, $H$ left | $CH_2OH$ | **D-Threose** ✓ | **Step 3: Confirm D-Configuration** D-sugars have the $OH$ group on the **right** at the **highest-numbered chiral center** (C3 in this case). Structure (4) has $OH$ on the right at C3, confirming D-configuration. At C2, the arrangement differs from D-erythrose, making this D-threose. **The answer is (4)** because it matches the stereochemistry of D-threose.