See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Optical Activity in Butanol Isomers **Understanding Optical Activity:** A compound exhibits optical activity only if it contains a chiral center (stereogenic center) — a carbon atom bonded to four different groups. **Analyzing Each Isomer:** 1. **n-butyl alcohol** ($CH_3CH_2CH_2CH_2OH$) - Linear chain with no chiral center - Not optically active ❌ 2. **Isobutyl alcohol** ($(CH_3)_2CHCH_2OH$) - Primary alcohol with no chiral center - Not optically active ❌ 3. **s-butyl alcohol** ($CH_3CH_2CH(OH)CH_3$) - The central carbon (marked *) bonded to: $-OH$, $-H$, $-CH_3$, $-CH_2CH_3$ - **Four different groups** → **chiral center present** ✓ - Exhibits optical activity (exists as (+) and (−) enantiomers) ✓ 4. **t-butyl alcohol** ($(CH_3)_3COH$) - Tertiary alcohol where central carbon has three methyl groups (identical) - Not optically active ❌ **Answer: (3) s-butyl alcohol** s-Butyl alcohol is the only butanol isomer with a stereogenic center, making it optically active and the simplest alkanol exhibiting this property.