Assertion: Plants possessing `C_(4)`- pathway of carbon fixation have a higher net primary productively than the `C_(3)`-pathway possessing plants.
Reason: For each unit weight of fixed carbon, `C_(4)`-pathway possessing plants require less water than `C_(3)` pathway possessing plants.

Options

A. If both Assertion and Reason are true and the Reason is a correct explanation of the Assertion.
B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
D. If Assertion is true but the Reason is false.

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts related to C3 and C4 pathways of carbon fixation in plants.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that plants with the C4 pathway of carbon fixation have a higher net primary productivity (NPP) compared to those with the C3 pathway.
- **Explanation**: C4 plants are adapted to high light intensity and temperature, and they can efficiently fix carbon dioxide even under conditions where C3 plants would struggle. This efficiency leads to higher rates of photosynthesis and, consequently, higher NPP.

2. **Understanding the Reason**:
- The reason given is that for each unit weight of fixed carbon, C4 plants require less water than C3 plants.
- **Explanation**: C4 plants have adaptations such as a more efficient use of water due to their ability to minimize photorespiration and their specialized anatomy (Kranz anatomy) that allows them to fix carbon dioxide more effectively. Therefore, they can produce the same amount of biomass while using less water compared to C3 plants.

3. **Evaluating the Truth of the Assertion**:
- The assertion is **true**. C4 plants generally exhibit higher NPP due to their efficient carbon fixation process.

4. **Evaluating the Truth of the Reason**:
- The reason is also **true**. C4 plants do require less water for the same amount of carbon fixed compared to C3 plants.

5. **Conclusion**:
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the statement is valid.

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

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