Final answer:
Basophils are the least common leukocytes in a blood smear of a healthy individual, representing less than one percent of the total leukocyte count, and have granules stained dark blue.
Step-by-step explanation:
In a blood smear of a healthy individual, the leukocyte you are least likely to encounter is the basophil. Basophils comprise less than one percent of the total leukocyte count, making them the rarest type of white blood cell in the circulation. In addition to their scarcity, basophils have large granules within their cytoplasm that absorb a basic (alkaline) dye, resulting in a dark blue stain that may obscure their two-lobed nucleus, a characteristic that can make them more difficult to identify under a microscope compared to other leukocytes like neutrophils, monocytes, or lymphocytes.