Which of the following is NOT a type of white blood cell?

Platelets are indeed not a type of white blood cell; rather, they are cell fragments involved in blood clotting. They originate from larger cells called megakaryocytes in the bone marrow and play a crucial role in hemostasis, which is the process that prevents and stops bleeding.

In contrast, neutrophils, eosinophils, and B cells are all types of white blood cells (leukocytes). Neutrophils are essential for the immune response, particularly in fighting bacterial infections, while eosinophils are involved in combating parasitic infections and play a role in allergic reactions. B cells are a type of lymphocyte responsible for producing antibodies and are integral to the adaptive immune system. Understanding the distinct roles of these cell types aids in recognizing how the immune system functions, further underscoring why platelets do not fit within the classification of white blood cells.