See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Electrophilic addition reactions on styrene derivatives proceed via the vinyl double bond (CH=CH2). The rate of electrophilic addition depends on the electron density at the double bond. Electron-donating groups (EDGs) increase electron density at the vinyl group (making it more reactive toward electrophiles), while electron-withdrawing groups (EWGs) decrease electron density (making it less reactive). Step 1: Classify the substituents by their electronic effect on the vinyl group through the benzene ring: - NH2 (amino group): Strong electron-donating group by resonance (+M effect). Greatly increases electron density at the double bond. - OH (hydroxyl group): Moderate electron-donating group by resonance (+M effect). Increases electron density at the double bond. - CH3 (methyl group): Weak electron-donating group by hyperconjugation/induction (+I effect). Slightly increases electron density. - NO2 (nitro group): Strong electron-withdrawing group by resonance (-M effect). Greatly decreases electron density at the double bond. Step 2: Rank the reactivity toward electrophilic addition (higher electron density = faster reaction): - d (NH2): Highest electron density at vinyl group → fastest rate - b (OH): Second highest electron density → second fastest - c (CH3): Slight electron donation → third - a (NO2): Lowest electron density → slowest rate Step 3: Decreasing order: d > b > c > a This matches option (c): d > b > c > a. Why other options fail: - Option (a) a > b > c > d: Incorrect, places EWG (NO2) as fastest, which is wrong. - Option (b) b > c > a > d: Incorrect, places NH2 last despite being the strongest EDG. - Option (d) b > d > c > a: Incorrect, places OH above NH2; NH2 is a stronger donor than OH. Therefore, the correct answer is C.