See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Degree of Unsaturation Terminology **Step 1: Define Degree of Unsaturation (DBE)** Degree of unsaturation quantifies the number of double bonds, triple bonds, and/or rings in a molecule. It's calculated using: $$\text{DBE} = \frac{2C + 2 + N - H - X}{2}$$ where $C$ = carbons, $H$ = hydrogens, $N$ = nitrogens, $X$ = halogens. **Step 2: Understand What It Represents** - A molecule with DBE > 0 has **fewer hydrogen atoms** than a saturated alkane would have - This deficiency of hydrogen atoms (not carbon) indicates unsaturation through $\pi$ bonds or rings **Step 3: Analyze the Options** - **(1) Index of carbon deficiency**: Incorrect — unsaturation doesn't indicate missing carbons; it's about hydrogen deficiency - **(2) Index of hydrogen deficiency**: **Correct** — DBE directly measures how many H atoms are "missing" compared to a saturated compound - **(3) Both (1) and (2)**: Incorrect — only hydrogen deficiency is relevant - **(4) None of these**: Incorrect **Answer: Option (2) — Index of Hydrogen Deficiency** Degree of unsaturation is specifically the **index of hydrogen deficiency** because it quantifies the reduction in hydrogen atoms relative to a fully saturated alkane of the same carbon skeleton.