Which of the following is an auxin

Options

A. Maleic acid
B. Abscisic acid
C. Pyruvic acid
D. Indole acetic acid

Explanation

To determine which of the following is an auxin, we need to analyze the options provided: Malic acid, FCC acid, pyruvic acid, and indole acetic acid.

### Step-by-Step Solution:

1. **Understand what auxins are**: Auxins are a class of plant hormones that play a crucial role in regulating various aspects of plant growth and development, such as cell elongation, root formation, and fruit development.

2. **Examine the options**:
- **Malic acid**: This is an organic acid that is involved in the Krebs cycle and is not classified as an auxin.
- **FCC acid**: This is not a recognized auxin; it is related to senescence in plants but does not fall under the category of auxins.
- **Pyruvic acid**: This is a key intermediate in several metabolic pathways, including glycolysis, but it is not an auxin.
- **Indole acetic acid (IAA)**: This is a well-known auxin and is one of the most important naturally occurring auxins found in plants.

3. **Identify the correct answer**: Among the options provided, indole acetic acid (IAA) is the only substance that is classified as an auxin.

4. **Conclusion**: Therefore, the answer to the question "Which of the following is an auxin?" is **indole acetic acid**, which corresponds to option D.

### Final Answer:
Indole acetic acid (IAA) is the auxin among the given options.

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