Assertion : The higher concentration of `O_2` in the atmosphere is inhibitory to photosynthesis. Reason; Rubisco binds to oxygen at high partial pressure of oxygen

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reson are false.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that a higher concentration of oxygen (O2) in the atmosphere is inhibitory to photosynthesis. This means that when there is more oxygen present, the process of photosynthesis is negatively affected.

2. **Understanding the Reason**:
- The reason provided is that Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) binds to oxygen at high partial pressures of oxygen. Rubisco is an enzyme that plays a crucial role in the process of photosynthesis by fixing carbon dioxide.

3. **Rubisco Activities**:
- Rubisco has two main activities:
- **Carboxylase Activity**: This occurs when Rubisco binds to carbon dioxide (CO2) and is essential for photosynthesis.
- **Oxygenase Activity**: This occurs when Rubisco binds to oxygen (O2) instead of carbon dioxide, leading to a process called photorespiration.

4. **Effect of High Oxygen Concentration**:
- When the concentration of oxygen is high, Rubisco is more likely to engage in its oxygenase activity rather than its carboxylase activity. This means that instead of fixing carbon dioxide for photosynthesis, it will bind to oxygen, resulting in the formation of phosphoglycolate and phosphoglycerate, which does not contribute to the photosynthetic process.

5. **Conclusion**:
- Since the assertion is true (higher oxygen concentration inhibits photosynthesis) and the reason is also true (Rubisco binds to oxygen at high partial pressures), we conclude that both statements are correct and the reason provided accurately explains the assertion.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.