The correct answer is A. Eosinophils.

The presence of multiple pustules on the trunk in this 1-day-old child is most consistent with erythema toxicum neonatorum. Scrapings, Gram stains, and pathologic evaluation of erythema toxicum neonatorum show numerous eosinophils, which is characteristic of this disease.

Histiocytes, lymphocytes, mast cells, and neutrophils are less likely to be seen in erythema toxicum neonatorum compared with eosinophils.

References:

Marchini G, Ulfgren AK, Loré K, Ståbi B, Berggren V, Lonne-Rahm S. Erythema toxicum neonatorum: an immunohistochemical analysis. Pediatr Dermatol. 2001;18(3):177-187.