MCQ 51
In a reaction where 5 g of substance A combines with 10 g of substance B to form 12 g of substance C, what happens to the mass?
A) Mass is lost.
B) Mass is gained.
C) Mass is conserved.
D) Mass is doubled.
Answer: C) Mass is conserved.
Explanation: According to the Law of Conservation of Mass, the total mass of reactants equals the total mass of products.
MCQ 52
If two elements combine in different ratios to form different compounds, which law is demonstrated?
A) Law of Conservation of Mass
B) Law of Definite Proportions
C) Law of Multiple Proportions
D) Dalton’s Law
Answer: C) Law of Multiple Proportions.
Explanation: This law illustrates that two elements can combine in various ratios to create different compounds.
MCQ 53
What is the molar mass of carbon dioxide (CO₂)?
A) 22 g/mol
B) 28 g/mol
C) 44 g/mol
D) 12 g/mol
Answer: C) 44 g/mol.
Explanation: The molar mass is calculated as 12 (C) + 2(16) (O) = 44 g/mol.
MCQ 54
Which statement describes the Law of Conservation of Mass?
A) Energy is neither created nor destroyed.
B) The number of protons does not change in a reaction.
C) Matter can change forms, but total mass remains constant.
D) Compounds can only form from elements in a fixed ratio.
Answer: C) Matter can change forms, but total mass remains constant.
Explanation: This law states that while the forms of matter may change, the total mass before and after a reaction remains unchanged.
MCQ 55
What is the empirical formula for C₆H₁₂O₆?
A) CH₂O
B) C₂H₄O₂
C) C₆H₁₂O₆
D) C₁H₁O₁
Answer: A) CH₂O.
Explanation: The empirical formula represents the simplest whole number ratio of elements, which is CH₂O for glucose.
MCQ 56
What happens to the atoms in a chemical reaction according to Dalton’s Atomic Theory?
A) They are destroyed.
B) They are created.
C) They are rearranged.
D) They change their identity.
Answer: C) They are rearranged.
Explanation: Atoms are not created or destroyed but rearranged during chemical reactions.
MCQ 57
What do the subscripts in a chemical formula indicate?
A) The temperature of the substance
B) The state of the substance
C) The number of atoms of each element
D) The energy level of electrons
Answer: C) The number of atoms of each element.
Explanation: Subscripts indicate how many atoms of each element are present in a compound.
MCQ 58
Which of the following pairs of substances illustrates the Law of Multiple Proportions?
A) H₂ and O₂
B) CO and CO₂
C) NaCl and KCl
D) CH₄ and C₂H₆
Answer: B) CO and CO₂.
Explanation: Carbon and oxygen combine in different ratios to form carbon monoxide (CO) and carbon dioxide (CO₂).
MCQ 59
How does the Law of Conservation of Mass apply to a closed system?
A) Mass can be created and destroyed.
B) Mass remains unchanged.
C) Mass changes form.
D) Mass can be lost to the environment.
Answer: B) Mass remains unchanged.
Explanation: In a closed system, the total mass of reactants equals the total mass of products, ensuring conservation.
MCQ 60
What is formed when iron reacts with oxygen?
A) Iron sulfate
B) Iron oxide
C) Iron chloride
D) Iron hydroxide
Answer: B) Iron oxide.
Explanation: The reaction of iron with oxygen forms iron oxide, commonly known as rust.
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