Triple response is shown by hormone

Options

A. Ethylene
B. CK
C. 2, 4-D
D. `GA_(3)`

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which hormone is responsible for the triple response in plants.

2. **Defining Triple Response**: The triple response is a growth response exhibited by seedlings when they encounter an obstacle. This response helps the seedling navigate around the obstacle.

3. **Identifying the Hormones**: The options provided are:
- Ethylene
- Cytokinin (CK)
- 4D (a synthetic form of auxin)
- Gibberellic acid (GAT)

4. **Role of Ethylene**: Ethylene is known to be produced by the stem tip of the seedling when it senses stress from an obstacle.

5. **Effects of Ethylene**: The triple response induced by ethylene includes:
- **Thickening of the stem**: The stem becomes thicker to provide more support.
- **Horizontal growth of the stem**: Instead of growing upwards, the stem starts to grow horizontally to avoid the obstacle.
- **Slowing down of stem elongation**: The elongation of the stem is reduced to conserve energy and redirect growth.

6. **Conclusion**: Based on the understanding of the triple response and the role of ethylene, the correct answer to the question is that the hormone responsible for the triple response is **ethylene**.

### Final Answer:
Triple response is shown by the hormone **ethylene**.

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