🧪 Chemistry MCQ Questions

Set – 3 | General Science & Competitive Exams

Click on each question to reveal answers & explanations

Q21. Which of the following materials is composed entirely of carbon?
  • (A) Kevlar
  • (B) Spider silk
  • (C) Graphene
  • (D) Lexan
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Correct answer is Graphene. Graphene is a single layer of carbon atoms arranged in a hexagonal lattice.
Q22. Which of the following is not considered an allotrope of carbon?
  • (A) Diamond
  • (B) Graphite
  • (C) Oxocarbon
  • (D) Kevlar
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Correct answer is Kevlar. Kevlar is a synthetic polymer, not a naturally occurring form of carbon.
Q23. Which element forms the largest number of known compounds?
  • (A) Carbon
  • (B) Hydrogen
  • (C) Nitrogen
  • (D) Oxygen
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Correct answer is Carbon. Carbon’s tetravalency allows it to form a vast variety of compounds.
Q24. Which of the following substances does not contain carbon?
  • (A) Diamond
  • (B) Graphite
  • (C) Coal
  • (D) Sodium chloride
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Correct answer is Sodium chloride. NaCl is an ionic compound composed of sodium and chlorine, no carbon.
Q25. Pencil “lead” is made of:
  • (A) Charcoal
  • (B) Graphite
  • (C) Lamp black
  • (D) Coal
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Correct answer is Graphite. Pencil cores are made from graphite, which is a form of carbon.
Q26. Heavy water differs from ordinary water because it:
  • (A) Contains deuterium instead of hydrogen
  • (B) Has more dissolved minerals
  • (C) Contains more dissolved air
  • (D) Contains organic impurities
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Correct answer is Contains deuterium instead of hydrogen. Heavy water (D₂O) contains deuterium atoms instead of normal hydrogen, making its molecular weight 20.
Q27. Who discovered heavy water?
  • (A) Heinrich Hertz
  • (B) H.C. Urey
  • (C) G. Mendel
  • (D) Joseph Priestley
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Correct answer is H.C. Urey. Harold C. Urey discovered deuterium and heavy water in 1931.
Q28. The molecular weight of heavy water (D₂O) is:
  • (A) 18
  • (B) 20
  • (C) 36
  • (D) 54
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Correct answer is 20. Heavy water contains deuterium (mass 2) instead of hydrogen (mass 1), so molecular weight = 2+2+16 = 20 g/mol.
Q29. Which catalyst is commonly used for hydrogenation of vegetable oils?
  • (A) Zinc
  • (B) Platinum
  • (C) Nickel
  • (D) Iron
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Correct answer is Nickel. Nickel is widely used as a catalyst for hydrogenation of vegetable oils.
Q30. Which of the following is an example of a carbon-rich material used in energy or writing applications?
  • (A) Coal
  • (B) Heavy water
  • (C) Lexan
  • (D) Platinum
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Correct answer is Coal. Coal is a carbon-rich material widely used in energy production.
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