Phytohormone responsible for 'Respiratory climactic ' is .

Options

A. ABA
B. Ethylene
C. `GA_(3)`
D. IAA

Answer

### Step-by-Step Solution:

1. **Understanding Respiratory Climactic**:
- Respiratory climactic refers to the increase in the rate of respiration in plants, particularly during certain developmental stages such as fruit ripening.

2. **Identifying the Phytohormones**:
- The question provides four options:
- A) Abscisic Acid (ABA)
- B) Ethylene
- C) Gibberellin (GA3)
- D) Indole-3-Acetic Acid (IAA)

3. **Analyzing the Role of Ethylene**:
- Ethylene is a gaseous plant hormone known for its role in the ripening of fruits. It acts as a plant growth regulator and is synthesized in large amounts during the ripening process.

4. **Connecting Ethylene to Respiratory Climactic**:
- The increase in respiration rate during fruit ripening is directly linked to the action of ethylene. As fruits ripen, ethylene promotes an increase in respiration, leading to what is termed as respiratory climactic.

5. **Conclusion**:
- Based on the analysis, ethylene is the phytohormone responsible for respiratory climactic due to its significant role in enhancing respiration during fruit ripening.

### Final Answer:
- The phytohormone responsible for 'Respiratory Climactic' is **Ethylene**.

---