Assertion :- During S-phase, amount of DNA per cell doubles.
Reason :- During S-phase, there is no increase in chromosome number.

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that during the S-phase of the cell cycle, the amount of DNA per cell doubles.
- This is true because the S-phase (Synthesis phase) is specifically the stage where DNA replication occurs, leading to the duplication of genetic material.

2. **Understanding the Reason**:
- The reason provided states that during the S-phase, there is no increase in chromosome number.
- This is also true. Although the DNA is replicated, the number of chromosomes remains the same because each chromosome is duplicated into two sister chromatids, but they are still counted as one chromosome until they are separated during cell division.

3. **Relationship Between Assertion and Reason**:
- The reason explains why the assertion is true. The doubling of DNA content during the S-phase does not lead to an increase in chromosome number because the chromosomes are simply replicated, not increased in number.

4. **Conclusion**:
- Both the assertion and the reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.

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