UPSC Prelims 2021 GS Paper I · Q21 of 98 Environment & Ecology easy

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

  1. (a) Congress grass
  2. (b) Elephant grass
  3. (c) Lemongrass ✓ UPSC's answer
  4. (d) Nut grass

Why the answer is (c)

• Lemongrass (Cymbopogon) yields citronella-type essential oils rich in citral and geraniol, which mosquitoes avoid; it is the base of natural repellent sprays, candles and coils — option (c).

• Congress grass (Parthenium) is an invasive weed causing allergies, not a repellent (a).

• Elephant grass (Napier) is a fodder crop (b); nut grass (Cyperus rotundus) is a persistent weed used in some traditional medicines, not as a repellent (d).

• Hence option (c).

Why the other options are wrong

(a) Congress grass
Parthenium is an allergenic invasive weed, not a repellent.
(b) Elephant grass
Napier grass is fodder, not a repellent.
(d) Nut grass
Nut grass is a weed, not a mosquito repellent.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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