![Q.24 Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]. Assertion [a]: The difference in the respective melting points of butter and coconut oil is caused by the degrees of saturation of the corresponding fatty acid chain. Reason [r]: Unsaturated fatty acid chains in fats/lipids become solid more easily because they are relatively straight and thus able to pack together more closely than saturated chain. (A) Both [a] and [r] are true and [r] is the correct reason for [a] (B) Both [a] and [r] are true but [r] is not the correct reason for [a] (C) Both [a] and [r] are false (D) [a] is true but [r] is false](https://www.letstalkacademy.com/wp-content/uploads/2025/12/slide_24-9.jpg)
Q.24 Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: The difference in the respective melting points of butter and coconut oil is
caused by the degrees of saturation of the corresponding fatty acid chain.
Reason [r]: Unsaturated fatty acid chains in fats/lipids become solid more easily because they
are relatively straight and thus able to pack together more closely than saturated chain.
(A) Both [a] and [r] are true and [r] is the correct reason for [a]
(B) Both [a] and [r] are true but [r] is not the correct reason for [a]
(C) Both [a] and [r] are false
(D) [a] is true but [r] is false
Answer: (D) [a] is true but [r] is false
Butter has a higher melting point (32–35°C) than coconut oil (24–25°C), and this difference arises from variations in their fatty acid saturation levels and chain lengths, making the assertion correct. However, the reason incorrectly states that unsaturated chains are straighter and pack better; saturated chains are actually straighter and pack more tightly, leading to higher melting points.
Fatty Acid Basics
Saturated fatty acids feature straight chains without double bonds, enabling close packing and stronger van der Waals forces for higher melting points. Unsaturated fatty acids contain kinks from cis double bonds, disrupting packing and resulting in lower melting points. Coconut oil (~90% saturated, mostly medium-chain like lauric acid C12:0) melts lower due to shorter chains despite high saturation.
Melting Points Comparison
| Fat | Melting Point (°C) | Saturated Fat % | Key Fatty Acids |
|---|---|---|---|
| Butter | 32–35 | ~64–68 | Longer chains (C16:0 palmitic) |
| Coconut Oil | 24–25 | ~90–92 | Shorter chains (C12:0 lauric) |
Butter’s longer saturated chains raise its melting point above coconut oil’s shorter ones.
Option Analysis
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(A) Incorrect: [r] is false, so it cannot explain [a].
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(B) Incorrect: [r] is false.
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(C) Incorrect: [a] is true, as saturation degrees (plus chain length) cause the melting point gap.
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(D) Correct: [a] holds true, but [r] reverses the chain shape logic.
Introduction to Butter vs Coconut Oil Melting Points
The difference in melting points of butter and coconut oil stems from fatty acid chain saturation, a key concept in biochemistry for exams like CSIR NET. Butter melts at 32–35°C, while coconut oil solidifies below 25°C, influencing their uses in cooking and industry. This article breaks down the science, corrects misconceptions on chain packing, and analyzes a classic Assertion-Reason question.
Role of Fatty Acid Saturation in Melting Points
Degrees of saturation determine how fats pack: saturated chains are linear for tight packing and high melting points; unsaturated kinks reduce this. Coconut oil’s high saturation (~90%, short chains) yields a low 24–25°C melt due to weaker interactions from chain length. Butter (~65% saturated, longer chains like C16:0) packs better at higher temperatures.
Why the Melting Point Difference Exists
Shorter medium-chain fatty acids (e.g., lauric in coconut oil) lower melting points despite saturation, as seen in comparisons with cocoa butter. Butter’s mix favors solidity up to body temperature, aiding mouthfeel. This fatty acid chain variation explains the gap, not just saturation alone.
Assertion-Reason Breakdown for CSIR NET
Assertion [a] (True): Saturation degrees cause the melting point difference.
Reason [r] (False): It wrongly claims unsaturated chains are “straight” and pack better—saturated do.
Correct option: (D) [a] true, [r] false. Ideal for competitive exams testing lipid structure.
