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 & reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both assertion & Reason are true but the reason is not the correct explanation of the assertion, them mark (2).
C. If assertion is true statement but reason is false, them mark (3).
D. If both assertion and reason are false statements, them mark (4).

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Annelids, arthropods, and molluscs are protostomial coelomates."
- **Definition**: Protostomial coelomates are animals whose mouth develops from the blastopore during embryonic development, and they possess a true coelom (body cavity).

2. **Analyzing the Phyla**:
- **Annelids**: These are segmented worms (e.g., earthworms) that exhibit protostomial development and have a true coelom.
- **Arthropods**: This phylum includes insects, arachnids, and crustaceans, which also develop mouth first and possess a true coelom.
- **Molluscs**: This group includes snails, clams, and squids, which similarly show protostomial development and have a true coelom.

3. **Conclusion on the Assertion**:
- Since all three phyla (Annelids, Arthropods, and Molluscs) indeed develop as protostomial coelomates, the assertion is **true**.

4. **Understanding the Reason**:
- The reason states: "All the three phyla include members with bilateral symmetry and true coelom."
- **Bilateral Symmetry**: This means that the body can be divided into two equal halves along one plane.
- **True Coelom**: A body cavity that is completely lined by mesoderm.

5. **Analyzing the Reason**:
- All three phyla do exhibit bilateral symmetry and possess a true coelom, thus making the reason statement **true** as well.

6. **Connecting Assertion and Reason**:
- Although both the assertion and reason are true, the reason does not explain why Annelids, Arthropods, and Molluscs are classified as protostomial coelomates. The reason merely states characteristics that these phyla share but does not clarify the developmental process that defines them as protostomial.

7. **Final Conclusion**:
- Therefore, the correct answer is: Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.