What is the principal cation in human blood?

During the process of blood clotting,fibrin is formed by:

Blood clotting is primarily caused by which of the following?

$A$ person injured in a road accident does not have a known blood group and requires an immediate blood transfusion. $A$ doctor friend offers to donate blood immediately. What would be the blood group of this doctor?

Which of the following conditions is responsible for Erythroblastosis fetalis?

Which of the following factors is responsible for the maturation of erythrocytes?