A person with unknown blood group under $ABO$ system, has suffered much blood loss in an accident and needs immediate blood transfusion. His one friend who has a valid certificate of his own blood type, offers for blood donation without delay. What would have been the type of blood group of the donor friend?

Which one of the following blood groups belongs to the category of universal recipient

A child has blood group $O .$ If the father has blood group $A$ and mother blood group $\mathrm{B},$ work out the genotypes of the parents and the possible genotypes of the other offsprings.

In a medico-legal case of accidental interchange between two babies in a hospital, the baby of blood group $A$ could not be rightly given to a people

Genotype of blood group $‘A'$ will be