The lowest melting point of an essential fatty acid is that of

Options

A. Linoleic acid
B. Linolenic acid
C. Arachidonic acid
D. Both B and C.

Answer

To determine which essential fatty acid has the lowest melting point among linoleic acid, linolenic acid, and arachidonic acid, we can analyze each fatty acid based on its structure and the number of double bonds it contains.

### Step-by-Step Solution:

1. **Identify the Fatty Acids**:
- **Linoleic Acid**: This is an 18-carbon essential fatty acid with **two double bonds**.
- **Linolenic Acid**: This is also an 18-carbon essential fatty acid but has **three double bonds**.
- **Arachidonic Acid**: This fatty acid contains **20 carbon atoms** and has **four double bonds**.

2. **Understand the Impact of Double Bonds on Melting Point**:
- The presence of double bonds in fatty acids introduces kinks in the fatty acid chains, preventing them from packing closely together. This results in lower melting points.
- Generally, the more double bonds a fatty acid has, the lower its melting point.

3. **Melting Points of Each Fatty Acid**:
- **Linoleic Acid**: Melting point is approximately **-5°C**.
- **Linolenic Acid**: Melting point is approximately **-11°C**.
- **Arachidonic Acid**: Melting point is approximately **-50°C**.

4. **Comparison of Melting Points**:
- Comparing the melting points:
- Linoleic Acid: -5°C
- Linolenic Acid: -11°C
- Arachidonic Acid: -50°C
- Arachidonic acid has the lowest melting point at -50°C.

5. **Conclusion**:
- Therefore, the essential fatty acid with the lowest melting point is **arachidonic acid**.

### Final Answer:
The lowest melting point of an essential fatty acid is that of **arachidonic acid**.

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