Assertion–Reason (Blood Groups):\nAssertion (A): A person with blood group O is called a universal donor.\nReason (R): Group O red blood cells do not carry A or B antigens.

Introduction / Context:
The question reviews ABO blood grouping concepts and the rationale behind the term “universal donor.”

Given Data / Assumptions:

• Group O means absence of A and B antigens on RBC surfaces.
• Discussion is within the simplified school context (neglecting Rh for brevity).

Concept / Approach:
Transfusion reactions arise when recipient antibodies bind to donor RBC antigens. Since group O lacks A/B antigens, the chance of an ABO incompatibility reaction for red cell transfusion is minimal, which is why O (particularly O negative) is termed “universal donor” in simplified treatments.

Step-by-Step Solution:
1) A: True in simplified/educational context (strictly, O negative is universal for packed RBCs).2) R: True—absence of A/B antigens underlies reduced risk of agglutination.3) R explains A because it cites the immunohematological basis.

Verification / Alternative check:
Real-world practice also considers the Rh factor and component transfusion protocols; nevertheless, the pedagogical principle holds.

Why Other Options Are Wrong:
Calling R false contradicts ABO fundamentals; calling A false ignores conventional terminology used in exams.

Common Pitfalls:
Confusing plasma transfusion rules (AB is plasma universal donor) with RBC transfusion.

Final Answer:
Both A and R are true, and R explains A.