Final answer:
The KOH treatment is typically used on biological samples suspected of fungal infection, allowing for easier identification under a microscope by dissolving non-fungal elements.
Step-by-step explanation:
The lab technician intern is likely to apply a 10% KOH (potassium hydroxide) solution to a biological sample for diagnostic purposes. This treatment with KOH is commonly used in a microbiology laboratory to help in the identification of fungal organisms by dissolving human tissue and cellular debris, leaving only the fungal elements visible under a microscope. Thus, the sample that would require treatment with KOH would be one suspected of having a fungal infection.