Chapter-9 Redox Reactions — Online MCQ Test
CHEMISTRY · Grade 10 · IGCSE cambridge
Practice Chapter-9 Redox Reactions with a free chapter-wise online MCQ test.
This chapter covers: Oxidation and reduction in terms of oxygen and electrons and identifying redox in reactions..
AI-generated questions from basic to board-exam level, with instant results and explanations.
Chapter-9 Redox Reactions — Important Questions & Answers
Which of the following best defines oxidation in terms of oxygen?
- A. Loss of oxygen from a substance
- B. Gain of oxygen by a substance
- C. Transfer of electrons to oxygen
- D. Formation of oxygen gas
Answer: B. Gain of oxygen by a substance
Oxidation in terms of oxygen is defined as the gain of oxygen by a substance. For example, when carbon burns to form carbon dioxide, carbon is oxidized.
Oxidation in terms of oxygen is defined as the gain of oxygen by a substance. For example, when carbon burns to form carbon dioxide, carbon is oxidized.
What is reduction in terms of electrons?
- A. Loss of electrons
- B. Gain of electrons
- C. Transfer of protons
- D. Decrease in atomic number
Answer: B. Gain of electrons
Reduction is defined as the gain of electrons by a substance. When a substance gains electrons, its oxidation state decreases, hence the term 'reduction'.
Reduction is defined as the gain of electrons by a substance. When a substance gains electrons, its oxidation state decreases, hence the term 'reduction'.
In the reaction: Zn + CuSO₄ → ZnSO₄ + Cu, identify the substance that is reduced.
- A. Zinc
- B. Copper sulfate
- C. Copper
- D. Sulfate ions
Answer: C. Copper
Copper ions (Cu²⁺) in copper sulfate gain electrons and are converted to copper metal, so copper is reduced. Zinc loses electrons and is oxidized.
Copper ions (Cu²⁺) in copper sulfate gain electrons and are converted to copper metal, so copper is reduced. Zinc loses electrons and is oxidized.
In the reaction: 2KMnO₄ + 10FeSO₄ + 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 8H₂O, which species acts as the oxidizing agent?
- A. FeSO₄
- B. KMnO₄
- C. H₂SO₄
- D. Fe₂(SO₄)₃
Answer: B. KMnO₄
KMnO₄ contains manganese in the +7 oxidation state, which is reduced to +2 in MnSO₄. The oxidizing agent is the substance that causes oxidation by accepting electrons, which is KMnO₄.
KMnO₄ contains manganese in the +7 oxidation state, which is reduced to +2 in MnSO₄. The oxidizing agent is the substance that causes oxidation by accepting electrons, which is KMnO₄.
In the reaction: 3Cu + 8HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO↑ + 4H₂O, how many electrons are transferred per copper atom?
- A. 1 electron
- B. 2 electrons
- C. 3 electrons
- D. 4 electrons
Answer: B. 2 electrons
Each Cu atom goes from 0 to +2 oxidation state, losing 2 electrons. Three Cu atoms lose 6 electrons total, and 2 N atoms (in HNO₃) go from +5 to +2, each gaining 3 electrons (6 total). This confirms 2 electrons per Cu atom on average.
Each Cu atom goes from 0 to +2 oxidation state, losing 2 electrons. Three Cu atoms lose 6 electrons total, and 2 N atoms (in HNO₃) go from +5 to +2, each gaining 3 electrons (6 total). This confirms 2 electrons per Cu atom on average.