Which of the following organs is known as the “graveyard” of RBCs?

Spleen

The correct answer is Option (3) - Spleen

Spleen is called the graveyard of RBCs because after completion of lifespan, RBCs are destroyed in spleen where they are ingested by free macrophages.

About 2.5 million of RBCs are destructed in one second. After ingestion of RBCs by macrophages, the haemoglobin is dissociated into haem and globin. Iron of haem is released which is further used in process of formation of blood. The haem is converted into bilirubin, a yellow or brown pigment.