Which fatty acid is liquid at room temperature

Options

A. Palmitic acid
B. Stearic acid
C. Arachidic acid
D. Linoleic acid.

Answer

To determine which fatty acid is liquid at room temperature, we need to understand the difference between saturated and unsaturated fatty acids.

### Step-by-Step Solution:

1. **Understand the Structure of Fatty Acids**:
- Fatty acids are long chains of carbon atoms with a carboxyl group (-COOH) at one end.
- They can be classified as saturated or unsaturated based on the types of bonds between the carbon atoms.

2. **Identify Saturated vs. Unsaturated Fatty Acids**:
- **Saturated fatty acids** have only single bonds between carbon atoms. This structure allows them to pack closely together, making them solid at room temperature.
- **Unsaturated fatty acids** contain one or more double bonds between carbon atoms. The presence of these double bonds creates kinks in the chain, preventing tight packing and resulting in a liquid state at room temperature.

3. **Evaluate the Given Options**:
- **Palmitic Acid**: A 16-carbon saturated fatty acid (solid at room temperature).
- **Stearic Acid**: An 18-carbon saturated fatty acid (solid at room temperature).
- **Arachidic Acid**: A 20-carbon saturated fatty acid (solid at room temperature).
- **Linoleic Acid**: An 18-carbon unsaturated fatty acid with two double bonds (liquid at room temperature).

4. **Conclusion**:
- Among the options, linoleic acid is the only unsaturated fatty acid, which means it is liquid at room temperature. Therefore, the correct answer is **linoleic acid**.

### Final Answer:
**Linoleic Acid** is the fatty acid that is liquid at room temperature.