### Related Formula pK_a = -log_10 K_a$pK_a = -\log_{10} K_a$ textHigher acidity implies textHigher K_a implies textLower pK_a$\text{Higher acidity} \implies \text{Higher } K_a \implies \text{Lower } pK_a$ ### Core Logic Comparing the acidic strength among given compounds: 1. Ethanol is least acidic due to lack of resonance stabilization in ethoxide ion implies pK_a = 15.9$\implies pK_a = 15.9$ (II). 2. Phenol forms resonance-stabilized phenoxide implies pK_a = 10.0$\implies pK_a = 10.0$ (I). 3. m$m$-Nitrophenol experiences -I$-I$ effect of -NO_2$-NO_2$ group implies pK_a = 8.3$\implies pK_a = 8.3$ (IV). 4. p$p$-Nitrophenol experiences both strong -R$-R$ and -I$-I$ effects, maximizing structural stability implies pK_a = 7.1$\implies pK_a = 7.1$ (III). ### Step 1: Assembly This yields the complete matching pattern: A-II, B-I, C-IV, D-III. ### Pattern Recognition Para nitro substitued positions create maximal charge delocalization through resonance, giving it the lowest pK_a$pK_a$ value out of the options. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Organic Compounds Containing Oxygen

### Related Formula textEster xrightarrowtextDIBAL-H textAldehyde$\text{Ester} \xrightarrow{\text{DIBAL-H}} \text{Aldehyde}$ ### Core Logic Breaking down the multistep pathway: * **Step A**: The ester group is selectively reduced to an aldehyde using textDIBAL-H$\text{DIBAL-H}$ at low temperature without affecting other domains. * **Step B**: An intramolecular Aldol condensation occurs in the presence of base (textNaOH$\text{NaOH}$) to generate the bicyclic alpha,beta$\alpha,\beta$-unsaturated carbonyl framework. * **Step C**: Clemmensen reduction (using amalgamated zinc and hydrochloric acid, textZn(Hg)/HCl$\text{Zn(Hg)/HCl}$) reduces the ketone group to a hydrocarbon block. ### Step 1: Verification The step-by-step mechanism proceeds precisely as illustrated below:

### Pattern Recognition DIBAL-H stops cleanly at the aldehyde phase from an ester precursor, preparing the molecule perfectly for subsequent aldol ring closures. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Organic Compounds Containing Oxygen