Assertion: Dark reaction occurs only at night in the stroma of chloroplast
Reason: `CO_(2)` fixation occurs only during `C_(3)` cycle.

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 reason are false.

Explanation

To solve the question, we need to evaluate the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states: "Dark reaction occurs only at night in the stroma of chloroplast."
- The term "dark reaction" refers to the light-independent reactions of photosynthesis, also known as the Calvin cycle or C3 cycle.
- It is important to note that these reactions do not require light to occur, but they can take place in the presence or absence of light. Therefore, the assertion is **incorrect** because it suggests that dark reactions only occur at night.

### Step 2: Analyze the Reason
The reason states: "CO₂ fixation occurs only during C3 cycle."
- CO₂ fixation is a part of both the C3 cycle and the C4 cycle. In the C3 cycle, CO₂ is fixed by the enzyme Rubisco, while in the C4 cycle, CO₂ is initially fixed into a 4-carbon compound (oxaloacetic acid) in mesophyll cells.
- Since CO₂ fixation occurs in both cycles, the reason is also **incorrect**.

### Step 3: Conclusion
Both the assertion and the reason are incorrect. The assertion does not accurately describe the conditions under which dark reactions occur, and the reason incorrectly limits CO₂ fixation to only the C3 cycle.

### Final Answer
Both the assertion and the reason are false.

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