🧪 Advanced Chemistry MCQs
Set – 4 | Practice Questions for General Science & Competitive Exams
Test your knowledge and uncover answers with detailed explanations
Q31. Which gas has the lowest percentage (by volume) in Earth’s atmosphere?
- (A) Oxygen
- (B) Nitrogen
- (C) Carbon dioxide
- (D) Argon
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Correct answer is Carbon dioxide. CO₂ has the lowest percentage (~0.04%) in the Earth’s atmosphere compared to nitrogen, oxygen, and argon.
Q32. For deep-sea diving, which gas is commonly mixed with oxygen for safe respiration?
- (A) Nitrogen
- (B) Helium
- (C) Xenon
- (D) Ammonia
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Correct answer is Helium. Helium is used with oxygen to prevent nitrogen narcosis and ensure safe deep-sea diving.
Q33. A mixture of which gases is typically used by professional divers in deep-sea exploration?
- (A) Oxygen-Hydrogen
- (B) Helium-Nitrogen
- (C) Helium-Oxygen
- (D) Oxygen-Acetylene
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Correct answer is Helium-Nitrogen. This mixture prevents nitrogen narcosis and oxygen toxicity for deep-sea divers.
Q34. What is the molecular geometry of sulphur hexafluoride (SF₆)?
- (A) Trigonal pyramid
- (B) Octahedral
- (C) Planar
- (D) Tetrahedral
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Correct answer is Octahedral. SF₆ has 6 bonding pairs around the sulfur atom, forming an octahedral geometry according to VSEPR theory.
Q35. Which of the following gases is highly soluble in water?
- (A) Carbon
- (B) Nitrogen
- (C) Ammonia
- (D) Iodine
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Correct answer is Ammonia. Ammonia (NH₃) is highly soluble in water due to its ability to form hydrogen bonds with water molecules.
Q36. Identify the compound that is not a Lewis acid:
- (A) AlCl₃
- (B) BF₃
- (C) NH₃
- (D) FeCl₃
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Correct answer is NH₃. NH₃ is a Lewis base, as it can donate a pair of electrons, unlike AlCl₃, BF₃, and FeCl₃ which are Lewis acids.
Q37. Soda water, prepared by dissolving carbon dioxide in water, is:
- (A) Acidic in nature
- (B) Basic in nature
- (C) An oxidising agent
- (D) A reducing agent
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Correct answer is Acidic in nature. CO₂ dissolves in water forming carbonic acid (H₂CO₃), making soda water acidic.
Q38. Which of the following acids does not contain oxygen?
- (A) Hydrochloric acid
- (B) Nitric acid
- (C) Sulphuric acid
- (D) All of the above
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Correct answer is Hydrochloric acid. HCl contains no oxygen atoms, whereas HNO₃ and H₂SO₄ are oxygen-containing acids.
Q39. “Neela thotha” is the common name for which chemical compound?
- (A) Copper sulphate
- (B) Calcium sulphate
- (C) Iron sulphate
- (D) Sodium sulphate
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Correct answer is Copper sulphate. “Neela thotha” is a common name for blue crystalline CuSO₄·5H₂O.
Q40. An unknown gas dissolves quickly in water, turns red litmus blue, and produces hydrogen chloride with a white flame. Identify the gas:
- (A) Ammonia
- (B) Sulphur dioxide
- (C) Nitric hydroxide
- (D) Carbon monoxide
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Correct answer is Ammonia. NH₃ is basic, dissolves quickly in water turning red litmus blue, and reacts with HCl producing white smoke (NH₄Cl).
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