Which one of the following is used in preparing a natural mosquito repellent?

1. The question asks to identify a plant used in preparing a natural mosquito repellent. 2. Congress grass (Parthenium) is an invasive weed and not typically used as a repellent. 3. Elephant grass is mainly used as fodder for livestock. 4. Lemongrass (Cymbopogon species) contains essential oils like citronellal and geraniol, which are well-known for their insect-repelling properties, particularly against mosquitoes. It is widely used in commercial and homemade natural mosquito repellents. 5. Nut grass (Cyperus rotundus) is considered a persistent weed, although it has some traditional uses, it is not primarily known as a mosquito repellent. Therefore, Lemongrass is the correct answer.