Which of the following is a weed killer?

Options

A. 2, 4-D
B. NAA
C. GA
D. ABA

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a substance that acts as a weed killer. We need to identify which of the provided options is specifically designed for this purpose.

2. **Identifying the Options**: The options given include various plant hormones and substances. We need to analyze each one to determine if it is a weed killer.

3. **Analyzing Auxin**: Auxin is a plant hormone that promotes growth. However, when present in excess, it can be toxic to plants, particularly dicots. Some synthetic auxins, like 2,4-D, are specifically used as herbicides (weed killers).

4. **Evaluating 2,4-D**: The substance 2,4-D is a synthetic auxin that is widely recognized for its effectiveness in controlling weeds, especially broadleaf weeds. This makes it a candidate for being a weed killer.

5. **Examining Other Options**:
- **NAA (Naphthalene Acetic Acid)**: This is another synthetic auxin but is primarily used to promote root growth, not as a weed killer.
- **Gibberellic Acid**: This hormone is involved in promoting growth and elongation in plants but does not function as a weed killer.
- **ABA (Abscisic Acid)**: This hormone plays a role in stress responses in plants and is not used as a weed killer.

6. **Conclusion**: Based on the analysis, the correct answer to the question is 2,4-D, as it is specifically designed to control weeds.

**Final Answer**: 2,4-D is a weed killer.

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