Which one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
Correct answer
Explanation
The correct answer is C, Fullerene. Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
The best-known fullerene, C₆₀ or buckminsterfullerene, is a closed cage of 60 carbon atoms arranged in 12 pentagons and 20 hexagons, like a football. It was discovered in 1985 by Kroto, Curl and Smalley, who won the 1996 Nobel Prize in Chemistry for it. Because each molecule is a closed cage, fullerenes have no dangling bonds at their edges where hydrogen or other atoms can attach, unlike graphite and amorphous carbon.
A is wrong because charcoal, made by burning wood in little air, is an impure amorphous carbon with ash and other matter.
B is wrong because coke, made by heating coal without air, still holds ash, sulphur and other impurities.
D is wrong because carbon black, the soot of incompletely burnt oil or gas, contains hydrogen and other impurities.
Exam tip: crystalline allotropes are diamond, graphite and fullerene; C₆₀ is buckminsterfullerene, named after the architect Buckminster Fuller.
Practice Questions
View allA planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
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Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
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Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →A lemon kept in water in a glass tumbler appears to be larger than its actual size. It is because of
- A.reflection of light
- B.scattering of light
- C.refraction of light
- D.polarization of light
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The lemon looks bigger because light from it bends as it passes from water through the curved glass into air.
Read the full explanation →Which one of the following conclusions could not be derived from Rutherford's α-particle scattering experiment?
- A.Most of the space in the atom is empty.
- B.The radius of the atom is about 10⁵ times the radius of the nucleus.
- C.Electrons move in a circular path of fixed energy called orbits.
- D.Nearly all the mass of the atom resides in the nucleus.
Show answer
. Orbits of fixed energy were proposed by Niels Bohr in 1913; Rutherford's experiment said nothing about the energy of electrons.
Read the full explanation →Which one of the following is the mechanism of action of oral contraceptive pills?
- A.They kill the egg.
- B.They kill the sperm.
- C.They kill the zygote.
- D.They inhibit the release of egg.
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. Oral contraceptive pills prevent pregnancy mainly by stopping the ovary from releasing an egg.
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