See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Alcohol Dehydration Mechanism **Step I:** Protonation of $-OH$ group - Forms an oxonium ion ($-OH_2^+$) - Acid-catalyzed step, very fast (acid is regenerated) **Step II:** Loss of water (carbocation formation) - Primary carbocation ($CH_3-\overset{+}{C}H-CH_3$) forms - Breaking $C-O$ bond requires significant energy - **Rate-determining step (RDS)** — SLOWEST **Step III:** 1,2-Hydride shift - Rearranges primary carbocation → secondary carbocation - Very fast (intramolecular rearrangement) **Step IV:** Deprotonation - Loss of $H^+$ to form alkene - Fast equilibrium step **Why Option B is correct:** The overall reaction rate is limited by the slowest elementary step. **Step II involves bond breaking** (formation of a high-energy primary carbocation intermediate), making it rate-determining. Step III (hydride shift) is exceptionally fast because it's an **intramolecular rearrangement** with a lower activation energy compared to bond-breaking processes. $$\boxed{\text{Step II (slowest) | Step III (fastest)}}$$ **Answer: (B)**