Questions about Direct Redox Reactions
Direct Redox Reactions – 20 Multiple-Choice Questions
Questions
1. What is a direct redox reaction?
A) A reaction where electrons move through a wire
B) A reaction that occurs only in basic solution
C) A reaction in which oxidation and reduction occur in the same vessel
D) A reaction involving only combustion
E) A reaction with no electron transfer
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2. In redox reactions, oxidation is defined as:
A) Gain of electrons
B) Loss of electrons
C) Gain of protons
D) Loss of neutrons
E) Loss of energy only
3. In redox reactions, reduction is defined as:
A) Gain of oxygen
B) Gain of electrons
C) Loss of electrons
D) Increase in oxidation number
E) Reaction with water
4. What happens to the oxidation number of an atom that is oxidized?
A) It decreases
B) It increases
C) It becomes zero
D) It doesn’t change
E) It becomes negative
5. In the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, which species is reduced?
A) Zn
B) Cu²⁺
C) Zn²⁺
D) Cu
E) Both Zn and Cu
6. In the same reaction, what is the oxidizing agent?
A) Zn
B) Cu
C) Cu²⁺
D) Zn²⁺
E) Water
7. What is the oxidation number of Cl in Cl₂?
A) –1
B) +1
C) 0
D) –2
E) +2
8. Which of the following is not a redox reaction?
A) H₂ + Cl₂ → 2HCl
B) Zn + 2HCl → ZnCl₂ + H₂
C) NaOH + HCl → NaCl + H₂O
D) 2Mg + O₂ → 2MgO
E) Fe + CuSO₄ → FeSO₄ + Cu
9. What is the reducing agent in the reaction: 2Mg + O₂ → 2MgO?
A) MgO
B) Mg
C) O₂
D) O²⁻
E) H₂O
10. In a direct redox reaction, how are electrons transferred?
A) Through a wire
B) Through an external circuit
C) Directly from one species to another
D) Through light
E) Via electricity only
11. Which element is oxidized in the reaction: 2Al + 3Cl₂ → 2AlCl₃?
A) Cl
B) Al
C) AlCl₃
D) Both Al and Cl
E) None
12. What is the correct balanced redox reaction for: Fe + Cu²⁺ → ?
A) Fe + Cu²⁺ → Fe²⁺ + Cu
B) Fe + Cu²⁺ → Fe³⁺ + Cu
C) 2Fe + 3Cu²⁺ → 2Fe³⁺ + 3Cu
D) Fe + 2Cu²⁺ → Fe²⁺ + 2Cu
E) Fe + Cu → FeCu
13. In redox reactions, the substance that gains electrons is:
A) Always a metal
B) The oxidizing agent
C) The reducing agent
D) A catalyst
E) An acid
14. Which of these is a typical example of a direct redox reaction?
A) Electrolysis of water
B) Combustion of hydrogen
C) Redox titration
D) Galvanic cell operation
E) Salt precipitation
15. Which pair correctly identifies oxidation and reduction?
A) Gain of electrons – loss of electrons
B) Gain of mass – loss of mass
C) Loss of electrons – gain of electrons
D) Increase in size – decrease in size
E) Gain of oxygen – gain of hydrogen
16. What is the oxidation number of O in H₂O?
A) 0
B) –1
C) –2
D) +1
E) +2
17. Which of the following is always true in a redox reaction?
A) Oxygen must be present
B) A gas is produced
C) Electrons are transferred
D) Energy is absorbed
E) Water is formed
18. In the reaction: 2Fe + 3Cl₂ → 2FeCl₃, what is the oxidation number of Fe in FeCl₃?
A) +1
B) +2
C) +3
D) 0
E) –3
19. Which element is reduced in: 2Na + Cl₂ → 2NaCl?
A) Na
B) Cl
C) NaCl
D) Both Na and Cl
E) None
20. What is the total number of electrons transferred in the balanced reaction: 2Al + 3Cl₂ → 2AlCl₃?
A) 1
B) 2
C) 3
D) 6
E) 9
- Questions on Assigning Oxidation Numbers and Changes in Reactions
- Questions about Identifying Redox Reactions
- Questions on Balancing Redox Reactions
Answer Key with Explanations
1. C – Direct redox reactions occur in one container; no external circuit needed.
2. B – Oxidation is loss of electrons.
3. B – Reduction is gain of electrons.
4. B – Oxidation number increases when a substance is oxidized.
5. B – Cu²⁺ is reduced to Cu (gains electrons).
6. C – The species that causes oxidation is the oxidizing agent, here Cu²⁺.
7. C – Elements in elemental form have oxidation number 0.
8. C – This is a neutralization reaction, not redox (no electron transfer).
9. B – Mg donates electrons = reducing agent.
10. C – In direct redox, electrons go directly from one reactant to another.
11. B – Al goes from 0 to +3 = oxidized.
12. A – Fe is oxidized to Fe²⁺; Cu²⁺ reduced to Cu.
13. B – Species gaining electrons causes oxidation = oxidizing agent.
14. B – Combustion is a common direct redox reaction.
15. C – Oxidation = loss; Reduction = gain of electrons.
16. C – Oxygen is usually –2 in compounds like H₂O.
17. C – Redox always involves electron transfer.
18. C – Fe in FeCl₃ has oxidation number +3.
19. B – Cl gains electrons → Cl⁻ (reduction).
20. D – Each Al gives 3 electrons → 2Al = 6 electrons total.
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