**Core Concept**
Pityriasis versicolor is a superficial fungal infection caused by Malassezia species, leading to hyperpigmentation and scaling. Treatment options for this condition focus on topical or systemic antifungal agents that inhibit fungal growth and proliferation.

**Why the Correct Answer is Right**
Griseofulvin is an antifungal medication, but it is primarily used for treating dermatophyte infections such as tinea capitis, tinea unguium, and tinea pedis. Griseofulvin does not have efficacy against Malassezia species, which are responsible for pityriasis versicolor. Therefore, it is not a suitable treatment option for this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Ketoconazole is an imidazole antifungal agent that is effective against Malassezia species. It can be used topically or orally for treating pityriasis versicolor.
**Option C:** Clotrimazole is another imidazole antifungal agent that is commonly used for treating fungal infections, including pityriasis versicolor. It is available in various formulations, including creams, shampoos, and oral tablets.
**Option D:** Selenium sulphate is a keratolytic agent that is sometimes used in combination with antifungal agents for treating pityriasis versicolor. It helps to remove scaling and improve the penetration of topical antifungal agents.

**Clinical Pearl / High-Yield Fact**
When treating pityriasis versicolor, it's essential to use antifungal agents that specifically target Malassezia species. Treatment with agents like ketoconazole or clotrimazole can help to clear the infection and prevent recurrence.

**✓ Correct Answer: B. Griseofulvin**