A : High concentration of atmospheric `SO_(2)` reduces primary productivity.
R : `SO_(2)` converts the chlorophyll a into phaeophytin.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are ture but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statements, then mark (4).

Answer

To solve the question regarding the assertion and reason about the effects of sulfur dioxide (SO2) on primary productivity and chlorophyll, we will break it down step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "high concentration of atmospheric SO2 reduces primary productivity."
- Primary productivity refers to the rate at which plants and other photosynthetic organisms produce organic compounds (like glucose) from carbon dioxide and water through photosynthesis. High levels of SO2 can negatively impact this process.

**Hint**: Recall that primary productivity is crucial for the energy flow in ecosystems and is primarily driven by photosynthesis.

2. **Understanding the Reason**:
- The reason states that "SO2 converts chlorophyll a into phaeophytin."
- Chlorophyll is the green pigment in plants that plays a critical role in photosynthesis. Phaeophytin is a form of chlorophyll that has lost its magnesium ion, which is essential for its function. The conversion of chlorophyll to phaeophytin can impair the plant's ability to photosynthesize effectively.

**Hint**: Consider the role of chlorophyll in photosynthesis and how its alteration can affect plant health and productivity.

3. **Connecting Assertion and Reason**:
- Both the assertion and reason are true. High levels of SO2 can lead to the conversion of chlorophyll into phaeophytin, which in turn reduces the plant's ability to carry out photosynthesis, thus lowering primary productivity.

**Hint**: Think about how the loss of chlorophyll function directly impacts the photosynthetic process.

4. **Conclusion**:
- Since both the assertion and reason are true, and the reason provides a correct explanation for the assertion, we can conclude that the correct option is that both assertion and reason are true, and the reason is the correct explanation of the assertion.

**Hint**: Look for the relationship between the two statements to determine if one logically explains the other.

### Final Answer:
Both assertion and reason are true, and the reason is the correct explanation of the assertion.