Assertion : The mantel of pearl oyster is three - layred.
Reason : Nacre- secreting cells are present just below the nacreous layer .

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

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that the mantle of the pearl oyster is three-layered. This is a factual statement about the anatomy of the pearl oyster, which belongs to the phylum Mollusca.

2. **Understanding the Reason**: The reason provided states that nacre-secreting cells are present just below the nacreous layer. This is also a true statement regarding the structure of the mantle, specifically about the cells responsible for secreting nacre, which contributes to the formation of pearls.

3. **Analyzing the Relationship**: While both the assertion and reason are true, we need to determine if the reason correctly explains the assertion. The assertion describes the structure of the mantle, while the reason describes the location of specific cells within that structure. However, the presence of nacre-secreting cells does not directly explain why the mantle is three-layered.

4. **Conclusion**: Since both statements are true but the reason does not provide a correct explanation for the assertion, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

5. **Final Answer**: The 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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