Which one of the following statements is not correct?
- A.All carbons in diamond are linked by carbon-carbon single bond.
- B.Graphite is layered structure in which layers are held together by weak van der Waals forces.
- C.Graphite layers are formed by hexagonal rings of carbon atoms.
- D.Graphite layers are held together by carbon-carbon single bond.
Correct answer
Explanation
The correct answer is D, graphite layers are held together by carbon-carbon single bond. The layers of graphite are held only by weak van der Waals forces, not by covalent bonds.
Diamond and graphite are allotropes of carbon. In diamond each carbon atom is bonded by single covalent bonds to four others in a rigid three-dimensional network, which makes it the hardest natural substance and a non-conductor. In graphite each carbon bonds to only three others, forming flat sheets of hexagonal rings; the fourth electron of each atom is free to move, so graphite conducts electricity. The sheets lie one over another and are attracted only weakly, so they slide easily, making graphite soft and slippery and useful as a lubricant and in pencils.
A is wrong as an answer because diamond's carbons are indeed joined by single bonds.
B is wrong as an answer because weak van der Waals forces do hold the layers together.
C is wrong as an answer because each graphite layer is a network of hexagonal rings.
Exam tip: diamond, four bonds per carbon, hard, non-conductor; graphite, three bonds, sliding layers, conductor.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
Show answer
Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
Show answer
They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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