See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: When dicarboxylic acids are heated, they may undergo decarboxylation or cyclodehydration (anhydride formation) depending on the geometry and chain length of the acid. Step 1 - Malonic acid (a): Malonic acid, HOOC-CH2-COOH, readily undergoes decarboxylation on heating to give acetic acid and CO2. So it is affected. Step 2 - Maleic acid (b): Maleic acid is the cis-butenedioic acid. Because the two carboxyl groups are on the same side of the double bond, they are held in close proximity. On heating, maleic acid readily undergoes intramolecular cyclodehydration to form maleic anhydride. So it is affected. Step 3 - Fumaric acid (c): Fumaric acid is the trans-butenedioic acid. Because the two carboxyl groups are on opposite sides of the double bond, they are far apart and cannot approach each other to form a cyclic anhydride. Fumaric acid cannot undergo decarboxylation easily either under moderate heating conditions. Thus, fumaric acid remains unaffected on heating (it only converts to maleic acid at very high temperatures, but under normal heating conditions it does not react). This is the key distinction: the trans geometry prevents anhydride formation. Step 4 - Succinic acid (d): Succinic acid, HOOC-CH2-CH2-COOH, on heating forms succinic anhydride (a five-membered cyclic anhydride) readily. So it is affected. Why other options fail: (a) decarboxylates, (b) forms anhydride due to cis geometry, (d) forms cyclic anhydride. Only fumaric acid (c) cannot form a cyclic anhydride due to its trans configuration and does not easily decarboxylate, so it remains unaffected on heating. Therefore, the correct answer is C.