Final answer:
In the Kleihaur-Betke apt test, fetal RBCs are resistant to pH changes, while maternal RBCs are sensitive, aiding in the diagnosis of conditions like HDN or erythroblastosis fetalis.
Step-by-step explanation:
In the Kleihaur-Betke apt test, fetal RBCs will be resistant to pH change, and maternal RBCs will be sensitive to pH change. Therefore, the correct answer to the question is a) Resistant; sensitive. This test differentiates between fetal and maternal blood cells by using an acid solution to elute the hemoglobin from adult hemoglobin-containing cells (maternal), while fetal cells, which contain fetal hemoglobin, remain intact due to their resistance to the acid. This property is utilized to diagnose fetal-maternal hemorrhage conditions, such as hemolytic disease of the newborn (HDN) or erythroblastosis fetalis, where Rh- mothers who are sensitized to Rh+ cells produce anti-Rh antibodies that can cross the placenta and destroy fetal RBCs.