**Core Concept**
Griseofulvin is an antifungal medication that works by inhibiting fungal cell division, specifically by binding to microtubules and preventing the formation of the mitotic spindle. This mechanism of action makes it effective against dermatophytes, a type of fungi that causes skin, hair, and nail infections.

**Why the Correct Answer is Right**
Griseofulvin is not useful in treating Tinea versicolor because it is caused by Malassezia yeast, which is not sensitive to griseofulvin. Tinea versicolor is a superficial fungal infection that affects the skin, causing patches of discoloration. Griseofulvin's mechanism of action is specific to dermatophytes, such as Trichophyton and Microsporum, which cause infections like Tinea capitis, Tinea cruris, and Tinea pedis.

**Why Each Wrong Option is Incorrect**
**Option A:** Tinea capitis is a fungal infection of the scalp, commonly caused by Trichophyton and Microsporum species. Griseofulvin is effective against these organisms and is often used to treat Tinea capitis.
**Option B:** Tinea cruris, also known as jock itch, is a fungal infection of the groin area. Griseofulvin is used to treat this condition, particularly in cases caused by Trichophyton and Microsporum species.
**Option D:** Tinea pedis, or athlete's foot, is a fungal infection of the foot. Griseofulvin is effective against the dermatophytes that cause Tinea pedis, making it a useful treatment option.

**Clinical Pearl / High-Yield Fact**
Griseofulvin is not absorbed orally and is not effective systemically, making it a topical treatment only. Its effectiveness is also limited by its narrow spectrum of activity against dermatophytes.

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