Which one of the following materials is not an allotrope of carbon ?
- A.Diamond
- B.Graphene
- C.Fly ash
- D.Fullerene
Correct answer
Explanation
The correct answer is C, Fly ash. Fly ash is the fine powdery residue left after coal is burnt in thermal power stations; it is a mixture of oxides, not a pure form of carbon.
Allotropes are different physical forms of the same element in which the atoms are bonded in different arrangements. Fly ash is made mostly of silica, alumina and iron oxide, with only a little unburnt carbon, and it is used in cement, bricks and road building. Carbon's allotropes include diamond, graphite, graphene, fullerenes and carbon nanotubes.
A is wrong because diamond is carbon in which each atom is bonded to four others in a rigid three-dimensional network, making it the hardest natural substance.
B is wrong because graphene is a single layer of carbon atoms arranged in hexagons, one sheet of graphite.
D is wrong because fullerenes are cage-like carbon molecules; the best known, C₆₀, is shaped like a football and is called buckminsterfullerene.
Exam tip: carbon allotropes: diamond, graphite, graphene, fullerene (C₆₀), nanotubes; fly ash is a coal-burning waste.
Practice Questions
View allThe hydrogen bomb and the uranium bomb are based, respectively on
- A.nuclear fusion and fission
- B.fission and thermonuclear fusion
- C.geothermal fission and fusion
- D.geothermal fusion and fission
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A hydrogen bomb fuses light hydrogen nuclei, while a uranium bomb splits heavy uranium-235 nuclei. In nuclear fission a heavy nucleus such as uranium-235 absorbs a neutron and splits into two lighter nuclei, releasing energy and two or three more neutrons.
Read the full explanation →In ovules of Angiosperms, which one of the following is not a haploid cell ?
- A.Nucellus
- B.Synergid
- C.Egg
- D.Antipodal
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The nucellus is the diploid tissue of the ovule itself, while the synergids, the egg and the antipodals are haploid cells of the embryo sac.
Read the full explanation →In a bipolar junction transistor
- A.all the three regions (the emitter, the base and the collector) have equal concentrations of impurity
- B.the emitter has the least concentration of impurity
- C.the collector has the least concentration of impurity
- D.the base has the least concentration of impurity
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The base is made thin and lightly doped so that most charge carriers from the emitter cross it to the collector.
Read the full explanation →Which one of the following types of glasses is used for making optical instruments?
- A.Pyrex glass
- B.Soft glass
- C.Hard glass
- D.Flint glass
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Flint glass contains lead oxide, which gives it a high refractive index and clarity, so it is used for lenses and prisms of optical instruments.
Read the full explanation →Lysosome is formed from which of the following cell organelles?
- A.Nucleus
- B.Endoplasmic reticulum
- C.Golgi bodies
- D.Ribosomes
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Lysosomes bud off from the Golgi apparatus as small membrane-bound sacs packed with digestive enzymes. The hydrolytic enzymes of a lysosome are first made on ribosomes attached to the rough endoplasmic reticulum.
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