Assertion : The primary `CO_(2)` acceptor in `C_(4)` pathway is 3-carbon molecule phosphoenol pyruvate (PEP).
Reason: The enzyme responsible for this fixation is PEP carboxylase or PEPcase.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion:**
- The assertion states that the primary CO₂ acceptor in the C₄ pathway is the 3-carbon molecule phosphoenolpyruvate (PEP).
- In the C₄ photosynthetic pathway, PEP indeed acts as the primary acceptor of CO₂.

2. **Understanding the Reason:**
- The reason provided states that the enzyme responsible for this fixation is PEP carboxylase (PEPcase).
- PEPcase is the enzyme that catalyzes the reaction where CO₂ is fixed to PEP, forming oxaloacetic acid (OAA).

3. **Analyzing the Relationship:**
- Both the assertion and the reason are correct statements.
- However, the reason does not fully explain the assertion because it does not address the broader context of the C₄ pathway and its adaptations.

4. **Conclusion:**
- The assertion is true: PEP is the primary CO₂ acceptor in the C₄ pathway.
- The reason is also true: PEP carboxylase is the enzyme that facilitates this reaction.
- However, the reason does not adequately explain why PEP is the primary CO₂ acceptor, as it lacks context regarding the overall C₄ pathway.

**Final Answer:**
- The assertion is true, and the reason is true, but the reason does not correctly explain the assertion.

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