Which is the primary cation present in the blood plasma?

The old and worn-out $RBCs$ are filtered out by:

Detection of blood group is done by an agglutination test using antiserum. According to this:

Assertion: The regulation of $RBC$ production is accomplished by $FSH$.
Reason: Erythropoietin hormone circulates to red bone marrow where it increases stem cell mitosis and speeds up the development of $RBCs$.

Which $\text{WBCs}$ are phagocytic cells that destroy foreign organisms entering the body?

Which blood group can be given to patients of any blood group?