Which of the following is 18-C unsaturated fatty acid with two double bonds?

Options

A. Oleic acid
B. Linolenic acid
C. Stearic acid
D. Linoleic acid

Answer

To determine which of the following is an 18-carbon unsaturated fatty acid with two double bonds, we will analyze the given options based on their structure and characteristics.

### Step-by-Step Solution:

1. **Identify the Characteristics of Fatty Acids**:
- Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).
- The number of carbon atoms in the chain is crucial for identification.

2. **Examine the Options**:
- We need to look at each option provided and check their carbon count and the number of double bonds.

3. **Analyze Oleic Acid**:
- Oleic acid is known to have 18 carbon atoms.
- It is an unsaturated fatty acid but has only **one double bond**.
- Therefore, it does not meet the criteria of having two double bonds.

4. **Analyze Linoleic Acid**:
- Linoleic acid also has **18 carbon atoms**.
- It is an unsaturated fatty acid and contains **two double bonds**.
- This matches the criteria we are looking for.

5. **Analyze Stearic Acid**:
- Stearic acid is a saturated fatty acid.
- It contains **18 carbon atoms** but has **no double bonds**.
- Thus, it does not meet the criteria.

6. **Conclusion**:
- The only fatty acid that fits the description of being an 18-carbon unsaturated fatty acid with two double bonds is **linoleic acid**.

### Final Answer:
The correct answer is **linoleic acid**.

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