Assertion : Annelids, arthropods, and molluscs are protostomial coelomates .
Reason : All the three phyla include members with bilateral symmetry and true coelom.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true ,but the Reason is not the correct explanation of the 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 1: Understand the Assertion
The assertion states that "Annelids, arthropods, and molluscs are protostomial coelomates."
- **Definition**: Protostomial coelomates are animals that develop a mouth from the blastopore during embryonic development and possess a true coelom (body cavity).
- **Examples**: Annelids (like earthworms), arthropods (like insects and crustaceans), and molluscs (like snails and octopuses) all fall under this category.

### Step 2: Understand the Reason
The reason states that "All three phyla include members with bilateral symmetry and true coelom."
- **Bilateral Symmetry**: This means that the body can be divided into two identical halves on either side of a central axis. Annelids, arthropods, and molluscs exhibit bilateral symmetry.
- **True Coelom**: A true coelom is a fluid-filled body cavity completely surrounded by mesoderm. All three phyla indeed possess a true coelom.

### Step 3: Evaluate the Relationship Between Assertion and Reason
- Both the assertion and the reason are true statements. However, the reason does not specifically explain why the assertion is true. The assertion is about being protostomial coelomates, while the reason discusses characteristics (bilateral symmetry and true coelom) that are common to these groups but do not directly justify their classification as protostomes.

### Conclusion
Since both the assertion and the reason are true, but the reason does not provide a correct explanation for the assertion, the correct answer is:
**Option B: Both assertion and reason are true, but the reason is not the correct explanation for the assertion.**

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