See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: The acidic strength of substituted benzoic acids depends on the electron-donating or electron-withdrawing nature of the substituent and its position relative to the carboxyl group. Step 1: Identify the substituents. - Benzoic acid: no substituent, reference compound. - p-Methoxybenzoic acid: -OCH3 group at para position. - o-Methoxybenzoic acid: -OCH3 group at ortho position. Step 2: Effect of -OCH3 at para position (p-methoxybenzoic acid). The methoxy group (-OCH3) is an electron-donating group (EDG) via resonance. At the para position, it donates electrons into the ring by resonance, which increases electron density at the carboxylate group, destabilizing the carboxylate anion (conjugate base). This makes it harder to release a proton, thus p-methoxybenzoic acid is less acidic than benzoic acid. Step 3: Effect of -OCH3 at ortho position (o-methoxybenzoic acid). At the ortho position, the methoxy group exerts both resonance (electron-donating) and inductive/field effects (electron-withdrawing through the sigma framework, since oxygen is electronegative). Additionally, the ortho effect (steric inhibition of resonance or direct inductive effect) means the electron-withdrawing inductive effect of oxygen dominates over its resonance donation at the ortho position. Furthermore, there is an intramolecular hydrogen bonding possibility and steric effects that can affect solvation of the anion. The net result of the ortho effect is that o-methoxybenzoic acid is more acidic than benzoic acid, and significantly more acidic than p-methoxybenzoic acid. Step 4: Establish the order. - p-Methoxybenzoic acid (ii): least acidic (EDG by resonance at para, destabilizes anion). - Benzoic acid (i): intermediate acidic strength. - o-Methoxybenzoic acid (iii): most acidic among the three (ortho effect: inductive EWG dominates, stabilizes anion). So increasing order of acidic strength: ii < i < iii, which corresponds to option (c). Why other options fail: - (a) i < ii < iii: incorrect because p-methoxy should be less acidic than benzoic acid, not more. - (b) iii < i < ii: incorrect because o-methoxy is more acidic than benzoic acid, not less. - (d) iii < ii < i: completely inverts the correct trend. Therefore, the correct answer is C.