Final answer:
The most abundant leukocyte is the neutrophil, and the least abundant is the basophil, making the correct answer d. neutrophils; basophils.
Step-by-step explanation:
The most abundant leukocyte found in the blood is the neutrophil, whereas basophils are considered the least abundant. Therefore, the correct answer to the question is d. neutrophils; basophils. Neutrophils comprise 50-70 percent of the total leukocyte count and play a crucial role in fighting bacterial infections.
Meanwhile, basophils make up less than one percent of leukocytes and are involved in inflammatory reactions and allergic responses. Neutrophils are identified by their multi-lobed nucleus and neutral staining granules, while basophils are recognized by their dark blue stained granules and two-lobed nucleus that is often obscured by the granules.