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

The correct answer is C) Lemongrass. Lemongrass oil, extracted from Cymbopogon species, contains citral and citronellal, volatile compounds that mosquitoes find repellent. This is why lemongrass oil appears in natural repellent sprays, candles and lotions, and why the Cymbopogon family, including citronella grass, forms the base of many plant-based repellents.

• Congress grass is Parthenium hysterophorus, an invasive weed (not a true grass) known for causing allergic dermatitis and hay fever. It has no repellent use.
• Elephant grass (Pennisetum purpureum) is a tall fodder and biomass crop studied for bioenergy and biogas, not for insect repellence.
• Nut grass (Cyperus rotundus) is a sedge and a stubborn farmland weed. Its tubers feature in traditional medicine, but it is not a mosquito repellent.

Core concept: plant-based repellents and biopesticides. This connects to vector-borne disease control (malaria, dengue, filariasis) and to the debate between synthetic repellents such as DEET and botanical alternatives. Mains angle: sustainable vector control and the use of traditional knowledge.

Trap: candidates pick Congress grass because the name sounds like a familiar Indian plant, or they mix up elephant grass with citronella. Remember that the repellent grasses belong to Cymbopogon.