Assertion : The first clinical gene for ADA therapy was given to cure SCID
Reason : The normal gene was delivered into the patient's cell using retroviral vector

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of 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 first clinical gene therapy for ADA (Adenosine Deaminase) was used to treat SCID (Severe Combined Immunodeficiency Disease).
- SCID is a genetic disorder that severely affects the immune system, making patients highly susceptible to infections.

2. **Understanding the Reason**:
- The reason provided explains that the normal ADA gene was delivered into the patient's cells using a retroviral vector.
- Retroviral vectors are commonly used in gene therapy to introduce new genes into cells because they can efficiently integrate the gene into the host cell's genome.

3. **Evaluating the Assertion**:
- The assertion is correct because the first successful gene therapy was indeed conducted to treat SCID by introducing a functional ADA gene into the patient's cells.

4. **Evaluating the Reason**:
- The reason is also correct. The method of using a retroviral vector to deliver the normal ADA gene into the patient's cells is a well-established technique in gene therapy.

5. **Determining the Relationship**:
- Although both the assertion and reason are true, the reason does not specifically explain why the assertion is true. The assertion stands on its own as a fact about the first clinical gene therapy, while the reason provides a method used in that therapy.

6. **Conclusion**:
- Based on the evaluation, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion. Thus, the answer is option B.