**Core Concept**
Grisefulvin is an antifungal medication primarily used to treat fungal infections of the skin, hair, and nails. It works by inhibiting fungal cell division, ultimately leading to the death of the fungal cells. Grisefulvin is effective against dermatophytes, a type of fungi responsible for various skin and nail infections.

**Why the Correct Answer is Right**
Tinea versicolor is a superficial fungal infection of the skin caused by Malassezia yeast, not dermatophytes. Grisefulvin is ineffective against yeast infections, including Tinea versicolor, because it targets the cell walls of dermatophytes, which are different from the cell walls of yeast. Malassezia yeast has a different cell wall composition, making Grisefulvin ineffective in treating Tinea versicolor.

**Why Each Wrong Option is Incorrect**
**Option A:** Grisefulvin is actually useful in treating Tinea capitis, a fungal infection of the scalp caused by dermatophytes.
**Option B:** Grisefulvin is effective in treating Tinea cruris, a fungal infection of the groin area also caused by dermatophytes.
**Option D:** Grisefulvin is useful in treating Tinea pedis, a fungal infection of the foot caused by dermatophytes.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Grisefulvin is not absorbed orally and is primarily excreted in the feces, which can lead to gastrointestinal side effects. This highlights the importance of considering the pharmacokinetics of medications when treating various infections.

**✓ Correct Answer: C. Tinea versicolor**