See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Geometric Isomerism Analysis Geometric isomerism (cis-trans) requires a **double bond with two different groups attached to each carbon** of the $C=C$ bond. **Checking each option:** **(A) 1,2-dichloro-1-pentene:** $CH_2=C(Cl)-CHCl-CH_2-CH_3$ - Double bond carbons: $CH_2$ and $C(Cl)$ have different substituents → **shows geometric isomerism** ✓ **(B) 1,3-dichloro-2-pentene:** $CH_2Cl-CH=C(CH_2Cl)-CH_2-CH_3$ - Double bond carbons: Both have **two hydrogen atoms** attached - Structure: $H-C(H)=C(CH_2Cl)-...$ - One carbon has $H$ and $H$ (same groups) → **does NOT show geometric isomerism** ✗ **(C) 1,1-dichloro-1-pentene:** $CCl_2=CH-CH_2-CH_2-CH_3$ - Double bond carbons: $CCl_2$ and $CH$ have different substituents → **shows geometric isomerism** ✓ **(D) 1,4-dichloro-2-pentene:** $CH_2Cl-CH=C(CH_3)-CH_2Cl$ - Double bond carbons: $CH$ and $C(CH_3)$ have different substituents → **shows geometric isomerism** ✓ **Answer: (B)** — 1,3-dichloro-2-pentene lacks the requirement of two *different* groups on at least one double bond carbon, so it cannot exhibit cis-trans isomerism.