Which antisera is used to detect the $Rh$ blood group?

If a drop of each of the following is placed on four separate slides,which one will not coagulate?

Which ion is essential for blood clotting?

Blood group $AB$ has

What is the average lifespan of blood platelets?

$A$ person with an unknown blood group under the $ABO$ system has suffered significant blood loss in an accident and requires an immediate blood transfusion. His friend,who has a valid certificate of his own blood type,offers to donate blood without delay. What would be the blood group of the donor friend?