See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Cis-Trans Isomerism Analysis **Requirement for cis-trans isomerism:** A double bond must have **two different groups attached to each carbon** of the $C=C$ bond. **Evaluating each option:** **(1) 1-butene:** $CH_2=CH-CH_2-CH_3$ - One carbon has two identical H atoms - Cannot show cis-trans isomerism ✗ **(2) 2-propene:** $CH_2=C(CH_3)_2$ - One carbon has two identical CH₃ groups - Cannot show cis-trans isomerism ✗ **(3) 2-butene:** $CH_3-CH=CH-CH_3$ - Each carbon of the double bond has two **different groups** - Left C: one $CH_3$ and one H - Right C: one $CH_3$ and one H - **Cis form:** both $CH_3$ on same side - **Trans form:** $CH_3$ groups on opposite sides - Shows cis-trans isomerism ✓ **(4) Benzene:** Aromatic ring with delocalized electrons - No distinct double bonds with substituents - Does not show geometric isomerism ✗ **Answer: (3) 2-butene** — it's the only compound where both carbons of the double bond have two different substituents, allowing for distinct spatial arrangements.