Final answer:
The most appropriate treatment option for the patient's sun rash with hypopigmented round macules is Ketoconazole (Nizoral).
Step-by-step explanation:
The most appropriate treatment option for this patient is Ketoconazole (Nizoral).
Based on the patient's symptoms of a "sun rash" with hypopigmented round macules on the chest, shoulder, and back, and the presence of hyphae and spores on a KOH slide, the likely diagnosis is tinea versicolor. Tinea versicolor is a fungal infection caused by the yeast Malassezia furfur. Ketoconazole is an antifungal medication that is effective in treating tinea versicolor.
Hydrocortisone 2.5%, Tazarotene, and Nystatin cream are not appropriate for treating tinea versicolor, as they do not target the fungal infection.