Assertion :- Secondary constriction is called as NOR.
Reason:- Nucleolus is associated with secondary constriction of chromosome.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False
D. If both Assertion & Reason are false.

Answer

To analyze the assertion and reason provided in the question, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Secondary constriction is called as NOR."
- NOR stands for "Nucleolar Organizer Region," which is indeed a region on a chromosome that is involved in the formation of the nucleolus.

2. **Understanding the Reason**:
- The reason states that "Nucleolus is associated with the secondary constriction of chromosome."
- This is true because the nucleolus forms around the NOR, which is located at the secondary constriction of certain chromosomes.

3. **Evaluating the Relationship**:
- Since the assertion is correct (secondary constriction is known as NOR) and the reason is also correct (nucleolus is associated with the secondary constriction), we need to determine if the reason correctly explains the assertion.
- The reason explains that the nucleolus is formed at the NOR, which supports the assertion.

4. **Conclusion**:
- Both the assertion and the reason are true, and the reason provides a correct explanation for the assertion. Therefore, the correct answer is that both statements are true and the reason is the correct explanation of the assertion.

### Final Answer:
The correct option is: **Both assertion and reason are true, and reason is the correct explanation of the assertion.**

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