See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Understanding Isomers **Definition:** Isomers are compounds with the same **molecular formula** but **different structural arrangements** of atoms. ## Step-by-step Analysis: **Step 1:** Isomers must have identical **molecular formulas** - Example: Both butane and isobutane have formula $C_4H_{10}$ - ✓ Option (3) is correct **Step 2:** Isomers have the **same** structural formula? - ✗ No — different structural arrangements define isomerism - Option (1) is incorrect **Step 3:** Isomers have **identical** chemical properties? - ✗ No — different structures lead to different reactivity patterns - Example: $n$-butane and 2-methylpropane have different boiling points and reactivity - Option (2) is incorrect **Step 4:** Isomers have **identical** physical properties? - ✗ No — different structures cause different physical properties (melting point, boiling point, density) - Example: ortho-, meta-, and para-xylene have different boiling points - Option (4) is incorrect ## Conclusion: **Isomers are essentially identical with their MOLECULAR FORMULA (Option 3)** — they share the same molecular composition but differ in atomic arrangement, leading to different structural, chemical, and physical properties.