See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: This reaction involves the treatment of phenylacetic acid (Ph-CH2-COOH) with NaOH and CaO upon heating (dry distillation / decarboxylation conditions), followed by acidification. Step 1 - Identify the reagents and their role: NaOH + CaO with heat is the classic condition for decarboxylation of a carboxylic acid (or its sodium salt). When a sodium carboxylate salt is heated with CaO (which acts as a base and dehydrating agent), the carboxylate loses CO2 to give the hydrocarbon with one fewer carbon. Step 2 - Mechanism: Phenylacetic acid (Ph-CH2-COOH) first reacts with NaOH to form sodium phenylacetate (Ph-CH2-COONa). Upon heating with CaO, decarboxylation occurs: Ph-CH2-COONa + CaO (heat) → Ph-CH3 + Na2CO3 (or CaCO3). The -COOH group is lost as CO2, and the remaining fragment Ph-CH2- gains a proton to give toluene (Ph-CH3). Step 3 - Role of step (2) H(+): Acidification simply ensures any salt is converted to neutral form; the organic product remains Ph-CH3 (toluene). Step 4 - Why other options fail: (a) Ph-CO2H (benzoic acid) would require oxidation, not decarboxylation. (b) Ph-CH2-OH (benzyl alcohol) would require reduction, not decarboxylation. (d) Cyclohexane ring would require complete reduction of the aromatic ring, which does not occur under these conditions. Therefore, the correct answer is C.