Solution:

• Blood group O (or blood group zero in some countries) individuals do not have either A or B antigens on the surface of their RBCs, and their blood serum contains IgM anti-A and anti-B antibodies.
• Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e., A, B, O or AB).
• If a patient needs an urgent blood transfusion, and if the time taken to process the recipient’s blood would cause a detrimental delay, O negative blood can be issued.
• Because it is compatible with anyone, O negative blood is often overused and consequently is always in short supply