MCQ 41
What is the mass ratio of hydrogen to oxygen in water (H₂O)?
A) 1:16
B) 2:16
C) 1:8
D) 1:2
Answer: C) 1:8.
Explanation: The mass of hydrogen (2 g) to oxygen (16 g) in water is 1:8.
MCQ 42
Which statement best describes the Law of Conservation of Mass?
A) Energy is transformed during reactions.
B) Atoms are rearranged but not created or destroyed.
C) Compounds can form in any ratio.
D) Mass can disappear during reactions.
Answer: B) Atoms are rearranged but not created or destroyed.
Explanation: This law states that during a chemical reaction, atoms are rearranged, but the total mass remains constant.
MCQ 43
Which of the following is an example of a synthesis reaction?
A) Decomposition of calcium carbonate
B) Combustion of methane
C) Formation of water from hydrogen and oxygen
D) Reaction of zinc with hydrochloric acid
Answer: C) Formation of water from hydrogen and oxygen.
Explanation: A synthesis reaction involves two or more reactants combining to form a single product, like water.
MCQ 44
Which of the following best describes a compound?
A) A mixture of elements
B) A substance formed by a fixed ratio of atoms
C) An element in its pure form
D) A physical combination of different substances
Answer: B) A substance formed by a fixed ratio of atoms.
Explanation: A compound is formed when two or more elements chemically combine in a fixed ratio.
MCQ 45
Which law states that different compounds can be formed from the same elements?
A) Law of Definite Proportions
B) Law of Multiple Proportions
C) Law of Conservation of Mass
D) Dalton’s Law
Answer: B) Law of Multiple Proportions.
Explanation: This law indicates that elements can combine in different ratios to form various compounds.
MCQ 46
In a balanced chemical equation, the coefficients represent:
A) The number of molecules involved.
B) The types of atoms present.
C) The physical states of reactants and products.
D) The energy changes during the reaction.
Answer: A) The number of molecules involved.
Explanation: Coefficients in a balanced equation indicate the relative number of molecules or moles of each substance.
MCQ 47
What is the main consequence of not balancing a chemical equation?
A) It can lead to incorrect calculations of mass.
B) It shows no relationship between reactants and products.
C) It prevents the reaction from occurring.
D) It changes the physical states of reactants.
Answer: A) It can lead to incorrect calculations of mass.
Explanation: An unbalanced equation does not accurately reflect the conservation of mass, leading to incorrect mass calculations.
MCQ 48
How many grams of oxygen are required to completely react with 2 grams of hydrogen to form water?
A) 8 g
B) 16 g
C) 2 g
D) 4 g
Answer: B) 16 g.
Explanation: The reaction H₂ + ½O₂ → H₂O shows that 2 g of hydrogen requires 16 g of oxygen for complete reaction.
MCQ 49
Which of the following compounds shows a 1:1 ratio of elements?
A) H₂O
B) NH₃
C) CO
D) CH₄
Answer: C) CO.
Explanation: Carbon monoxide (CO) has a 1:1 ratio of carbon to oxygen atoms.
MCQ 50
What does the Law of Definite Proportions ensure about a compound?
A) Its elements can vary in proportion.
B) It will always have the same mass ratio of its elements.
C) Its properties change with the source.
D) It can exist in multiple forms.
Answer: B) It will always have the same mass ratio of its elements.
Explanation: This law guarantees that a compound has a fixed composition regardless of its source.
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