Assertion :- Trisomy or monosomy situation leads to a very serious consequence in the individual.
Down's syndrome is the trisomy of chromosome-21

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Trisomy or monosomy situation leads to a very serious consequence in the individual."
- Trisomy refers to the presence of an extra chromosome (for example, having 47 chromosomes instead of the normal 46), while monosomy refers to the absence of one chromosome (having 45 chromosomes instead of 46).
- Both conditions can lead to various developmental and health issues.

2. **Understanding the Reason**:
- The reason provided is "Down's syndrome is the trisomy of chromosome 12."
- However, Down's syndrome is actually caused by the trisomy of chromosome 21, not chromosome 12. This is a critical error in the reason.

3. **Evaluating the Truth of the Assertion and Reason**:
- The assertion is true because both trisomy and monosomy can lead to serious health consequences, such as developmental delays and other physical and mental impairments.
- The reason is false because it incorrectly identifies the chromosome associated with Down's syndrome.

4. **Conclusion**:
- Since the assertion is true and the reason is false, we conclude that the assertion is correct, but the reason does not correctly explain the assertion.

### Final Answer:
- **Assertion**: True
- **Reason**: False
- Therefore, the correct option is that the assertion is true, but the reason is false.