Assertion (A): Transplantation of organs to save certain patients often fail.
Reason (R): Blood vascular system and blood groups are responsible for such failures.

Options

A. Both A and R are true and R is the correct explanation for A.
B. Both A and R are true, but R is not the correct explanation for A.
C. A is true and R is false.
D. A is false and R is true.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Assertion (A):** The assertion states that organ transplantation often fails in certain patients. This is a true statement as organ transplants can indeed be rejected by the recipient's body.

2. **Understanding the Reason (R):** The reason provided is that the blood vascular system and blood groups are responsible for such failures. This statement is also true because blood type compatibility is crucial in organ transplantation to prevent rejection.

3. **Linking Assertion and Reason:** While both statements are true, the reason does not fully explain the assertion. The failure of organ transplantation is primarily due to the immune response of the recipient's body, which can be influenced by factors beyond just blood groups, such as tissue compatibility and the immune system's recognition of foreign cells.

4. **Evaluating the Options:**
- Option 1: Both assertion and reason are true, and the reason is a correct explanation of the assertion. (Incorrect)
- Option 2: Both assertion and reason are true, but the reason is not the correct explanation of the assertion. (Correct)
- Option 3: Assertion is true, and reason is false. (Incorrect)
- Option 4: Assertion is false, and reason is true. (Incorrect)

5. **Conclusion:** The correct answer is Option 2, as both the assertion and reason are true, but the reason does not adequately explain why organ transplantation often fails.