Which of the following blood groups is known as a universal donor in blood transfusion?

Blood group O.

The correct answer is Option (4)- Blood group O.

ABO grouping is based on the presence or absence of two surface antigens (chemicals that can induce immune response) on the RBCs namely A and B. Similarly, the plasma of different individuals contains two natural antibodies (proteins produced in response to antigens). Person with blood group ‘O’ have nil antigens on their RBCs and anti-A, B antibodies in plasma. Therefore, can donated blood to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors'.

From the above mentioned table it is evident that group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors’. Persons with ‘AB’ group can accept blood from persons with AB as well as the other groups of blood. Therefore, such persons are called ‘universal recipients’.