**Core Concept**
Chemoprophylaxis of malaria involves the use of antimalarial medications to prevent the development of the disease in individuals who have been exposed to infected mosquitoes. This approach is essential for travelers to endemic areas and for people living in regions where malaria is common. The choice of antimalarial medication depends on several factors, including the type of malaria, the destination, and the individual's medical history.

**Why the Correct Answer is Right**
The correct answer is based on the effectiveness and safety of various antimalarial medications. Atovaquone-proguanil (Malarone) and doxycycline are commonly used for chemoprophylaxis, while mefloquine (Lariam) is also an option. However, chloroquine is generally not recommended for chemoprophylaxis due to widespread resistance among Plasmodium falciparum parasites.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because atovaquone-proguanil (Malarone) is a well-established and effective antimalarial medication for chemoprophylaxis.
**Option B:** This option is incorrect because doxycycline is a commonly used antibiotic for chemoprophylaxis against malaria, particularly in areas with chloroquine resistance.
**Option C:** This option is incorrect because mefloquine (Lariam) is an alternative antimalarial medication for chemoprophylaxis, although it has a higher risk of neurological side effects.

**Clinical Pearl / High-Yield Fact**
When prescribing antimalarial medications for chemoprophylaxis, it's essential to consider the individual's travel itinerary, medical history, and potential drug interactions. A thorough risk-benefit assessment and regular monitoring are necessary to ensure the safe and effective use of these medications.

**Correct Answer: D. Chloroquine**