Lemongrass (Cymbopogon citratus) is used in preparing natural mosquito repellents due to its high citronella content, which has been scientifically shown to deter mosquitoes effectively. This aligns with the UPSC Prelims context of environmental sustainability and the use of natural resources, highlighting the importance of utilizing indigenous plants in pest control while minimizing reliance on synthetic chemicals. Such knowledge promotes a greater understanding of biodiversity and the role of traditional practices in promoting public health and environmental conservation.