The correct answer is A. Doxycycline.

The patient is presenting with signs of photo-onycholysis and photosensitivity most likely secondary to oral doxycycline, which is a treatment used for inflammatory and pustular acne. Within the tetracylcine antibiotic class, demeclocycline is more photosensitizing, followed by doxycycline, then tetracycline, and minocycline is the least photosensitizing.

Topical clindamycin, topical azelaic acid, benzoyl peroxide wash and acetaminophen are not strong photosensitizing medications that are known to cause photo-onycholysis.

References:

Passier A, Smits-van Herwaarden A, van Puijenbroek E. Photo-onycholysis associated with the use of doxycycline. BMJ. 2004;329(7460):265. doi:10.1136/bmj.329.7460.265