A : Tropical plants are more efficient in `CO_(2)` untilization.
R : `C_(4)` plants ensure that RuBisCO functions as carboxylase minimising oxygenase acitivity.

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Tropical plants are more efficient in CO2 utilization."
- This implies that tropical plants have mechanisms that allow them to utilize carbon dioxide more effectively than other types of plants.

2. **Understanding the Reason (R)**:
- The reasoning states that "C4 plants ensure that RuBisCO functions as carboxylase, minimizing oxygenase activity."
- This means that C4 plants have adapted in such a way that the enzyme RuBisCO, which is responsible for fixing carbon dioxide, is more efficient in the presence of CO2 and less affected by oxygen, which can lead to photorespiration.

3. **Linking Assertion and Reason**:
- C4 plants, which are often found in tropical regions, have a unique structure called Kranz anatomy. In this structure, RuBisCO is located in the bundle sheath cells where oxygen concentration is low, thus enhancing the efficiency of CO2 fixation.
- While many tropical plants are C4 plants, not all C4 plants are tropical. Therefore, while both statements are true, the reasoning does not directly explain the assertion.

4. **Conclusion**:
- Both the assertion and reasoning are true statements. However, the reasoning does not serve as a correct explanation for the assertion. They are independent truths.

### Final Answer:
- The assertion (A) is true, and the reason (R) is also true, but R is not the correct explanation of A.