**Core Concept**
The question is testing the knowledge of schizontocidal drugs, which are used to treat malaria caused by Plasmodium species. These drugs target the schizont stage of the parasite's life cycle, which is essential for its replication and survival.

**Why the Correct Answer is Right**
The correct answer is **Atovaquone**. Atovaquone is a fast-acting schizontocidal drug that works by inhibiting the electron transport chain in the parasite's mitochondria, leading to the disruption of ATP production and eventual death of the parasite. This mechanism of action is particularly effective against the Plasmodium species that cause malaria.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Artemisinin** is a fast-acting antimalarial drug that targets the blood stage of the parasite, but its action is not limited to schizontocidal activity.
* **Option B:** **Mefloquine** is an antimalarial drug that targets the blood stage of the parasite, but it is not as fast-acting as atovaquone.
* **Option C:** **Chloroquine** is an antimalarial drug that targets the blood stage of the parasite, but it is not as effective against certain strains of Plasmodium species.

**Clinical Pearl / High-Yield Fact**
Atovaquone is often used in combination with proguanil to treat malaria, and its fast-acting schizontocidal activity makes it an essential component of antimalarial therapy.

**Correct Answer:** C. Atovaquone.