Assertion : In `C_4` cycle, first stable product has 4 carbon compound
Reason : In `C_4` plants, `C_3` cycle is absent

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.

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that in the C4 cycle, the first stable product is a 4-carbon compound.
- This is true because the first stable product formed in the C4 pathway is oxaloacetic acid (OAA), which is a 4-carbon compound.

2. **Understanding the Reason**:
- The reason states that in C4 plants, the C3 cycle (Calvin cycle) is absent.
- This statement is false. While C4 plants have a modified pathway that enhances efficiency in carbon fixation, the C3 cycle is not completely absent; it is present but operates less efficiently compared to C4 plants.

3. **Evaluating the Relationship**:
- Since the assertion is true and the reason is false, we conclude that the reason does not correctly explain the assertion.

4. **Identifying the Correct Option**:
- Based on the analysis, the correct option is that the assertion is true, but the reason is false.

### Final Answer:
- The correct option is: **Assertion is true, but the reason is false.**