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1. Which law states that matter can neither be created nor destroyed during a chemical reaction?

• A. Law of Conservation of Energy
• B. Law of Conservation of Mass
• C. Law of Constant Composition
• D. Law of Multiple Proportions

Correct answer: B

Rationale: The correct answer is B, the Law of Conservation of Mass. This law, formulated by Antoine Lavoisier, states that matter cannot be created or destroyed in a chemical reaction. It is a fundamental principle in chemistry that explains the preservation of mass during chemical reactions, indicating that the total mass of the reactants is equal to the total mass of the products. The other choices are incorrect because: A: The Law of Conservation of Energy states that energy cannot be created or destroyed, not matter. C: The Law of Constant Composition refers to compounds having the same composition by mass regardless of their source or how they were prepared, not about the conservation of matter in reactions. D: The Law of Multiple Proportions describes the ratios in which elements combine to form compounds, not the conservation of mass.

2. What are the products of combustion of a hydrocarbon in excess oxygen?

• A. Carbon dioxide and water
• B. Naphthalene
• C. Chlorine and bromine
• D. Carbonium ions

Correct answer: A

Rationale: The correct answer is A: Carbon dioxide and water. During the combustion of a hydrocarbon in excess oxygen, the hydrocarbon reacts to produce carbon dioxide and water vapor as the final products. This reaction is known as complete combustion, where the hydrocarbon combines with oxygen to form carbon dioxide and water. Choices B, C, and D are incorrect because naphthalene is a specific hydrocarbon compound, chlorine and bromine are not typically formed during the combustion of hydrocarbons in excess oxygen, and carbonium ions are not the products of this reaction.

3. What is the product of the decomposition of water?

• A. Hydrogen and oxygen
• B. Carbon dioxide
• C. Nitrogen and hydrogen
• D. Methane

Correct answer: A

Rationale: The correct answer is A: Hydrogen and oxygen. When water undergoes decomposition, it breaks down into hydrogen and oxygen gases through a process known as electrolysis. This reaction is represented by 2H₂O → 2H₂ + O₂. Choice B, carbon dioxide, is incorrect as it is not a product of water decomposition. Choice C, nitrogen and hydrogen, is incorrect as water decomposes into hydrogen and oxygen, not nitrogen. Choice D, methane, is incorrect as methane is not a product of water decomposition.

4. What are negatively charged ions called?

• A. Neutrons
• B. Protons
• C. Anions
• D. Cations

Correct answer: C

Rationale: Negatively charged ions are called anions. Anions gain electrons and carry a negative charge, which distinguishes them from cations that are positively charged and neutrons and protons that are subatomic particles found in the nucleus of an atom. Choice A, Neutrons, are neutral subatomic particles found in the nucleus of an atom, not negatively charged ions. Choice B, Protons, are positively charged subatomic particles found in the nucleus of an atom, not negatively charged ions. Choice D, Cations, are positively charged ions that lose electrons, which is opposite to the behavior of negatively charged ions.

5. How many neutrons are in an atom of carbon-12?

• A. 2
• B. 4
• C. 6
• D. 24

Correct answer: C

Rationale: An atom of carbon-12 has 6 neutrons. The atomic number of carbon is 6, representing the number of protons. The atomic mass of carbon-12 is 12. To find the number of neutrons, subtract the atomic number from the atomic mass: 12 - 6 = 6 neutrons. Choice A, 2, is incorrect as it does not reflect the correct calculation for neutrons in carbon-12. Choice B, 4, is incorrect as it does not match the correct number of neutrons in carbon-12. Choice D, 24, is incorrect as it is significantly higher than the actual number of neutrons in carbon-12.

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