Quinine, the effective medicine in the treatment of malaria, is extracted from

Quinine is an alkaloid obtained from the bark of Cinchona trees (species such as Cinchona ledgeriana, C. calisaya and C. officinalis). That makes B correct.

• A (Cinnamon bark): Cinnamomum bark yields cinnamon spice and cinnamon oil, rich in cinnamaldehyde. It contains no quinine.
• C (Ocimum leaves): Ocimum, the tulsi genus, gives leaves used in traditional medicine and yields eugenol-rich oil. It is not a source of quinine.
• D (Acacia catechu bark): The khair tree gives catechu (katha), a tannin-rich astringent used in paan and dyeing. It is not an antimalarial source.

The core concept is plant-derived drugs and the cinchona alkaloids, which include quinine and quinidine. Quinine was the first effective antimalarial for a long time, and its history of cinchona cultivation in the Nilgiris and Bengal under British rule is a good Modern India and economic history link. For Mains, you can connect it to the shift from natural to synthetic antimalarials and to artemisinin from Artemisia annua, a later plant-based drug.

Trap: Aspirants see the word bark and pick cinnamon because it is the more familiar plant. Remember the chain of cinchona to quinine and cinchona to malaria.