See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Decreasing Order of Acidic Strength **Key Principle:** Phenolic acidity depends on: - **Electron-withdrawing groups** (EWG) → increase acidity by stabilizing the conjugate base - **Electron-donating groups** (EDG) → decrease acidity by destabilizing the conjugate base --- ## Analysis of Each Compound | Compound | Structure | Effect | Relative Acidity | |----------|-----------|--------|------------------| | **(I)** | 3,5-dimethylphenol | Two EDG ($CH_3$) → stabilize $OH$ | **Weakest** | | **(II)** | 2,4-dimethyl-6-nitrophenol | Mixed: EDG ($2\times CH_3$) + EWG ($NO_2$) | Moderate | | **(III)** | 2-nitrophenol | Single EWG ($NO_2$) → stabilizes conjugate base | **Very Strong** | | **(IV)** | 4-nitrophenol | Single EWG ($NO_2$) ortho/meta positioning | **Strongest** | | **(V)** | 2,6-dimethyl-4-nitrophenol | Mixed: EDG ($2\times CH_3$) + EWG ($NO_2$) | Weaker than III | --- ## Detailed Reasoning - **IV > III:** Para-substituted $NO_2$ is more effective than ortho (no steric hindrance on conjugate base) - **III > II:** One $NO_2$ stronger than two $CH_3$ groups diluting its effect - **II > V:** In II, $NO_2$ is para to $OH$ (more effective); in V, methyl groups are ortho to $OH$ (more deactivating) - **V > I:** One $NO_2$ outweighs two $CH_3$ groups $$\boxed{\text{Order: IV > III > II > V > I}}$$ **Answer: (A) $\text{I} > \text{III} > \text{IV} > \text{II} > \text{V}$** is incorrect based on this analysis. The **correct decreasing order** should be **IV > III > II > V > I**, which matches the principle that EWG increases phenolic acidity.