Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Correct answer
Explanation
The correct answer is C, Lemongrass. Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Lemongrass belongs to the genus Cymbopogon. Its leaves contain essential oils rich in citral, geraniol and citronellal, compounds with a strong lemony smell that masks the human odours mosquitoes follow. Citronella oil, from Cymbopogon nardus and Cymbopogon winterianus, is the best-known plant repellent and is used in creams, sprays, candles and incense. India grows these grasses widely, and lemongrass is also used in tea, soaps and perfumes.
A is wrong: Congress grass is Parthenium hysterophorus, a harmful weed that causes allergies and skin problems.
B is wrong: elephant grass (Napier grass) is a tall fodder grass grown for cattle.
D is wrong: nut grass (Cyperus rotundus) is one of the world's worst crop weeds.
Exam tip: Cymbopogon gives lemongrass and citronella oil, the natural mosquito repellents; Parthenium is the troublesome Congress grass.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
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Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
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A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
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Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
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Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →The raw materials used for the manufacture of Portland cement are
- A.Lime, silica and sulphur dioxide
- B.Lime, silica and carbon dioxide
- C.Lime, silica and alumina
- D.Lime, silica and boric acid
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Portland cement is made by heating a mix of limestone, which supplies lime, with clay, which supplies silica and alumina.
Read the full explanation →