Questions about Identifying Redox Reactions
Multiple-Choice Questions – Identifying Redox Reactions
1. What characterizes a redox reaction?
A) Exchange of protons
B) Formation of water
C) Change in oxidation states
D) Formation of gas only
E) Dissolution of a salt
2. Which reaction is a redox reaction?
A) HCl + NaOH → NaCl + H₂O
B) AgNO₃ + NaCl → AgCl + NaNO₃
C) Zn + CuSO₄ → ZnSO₄ + Cu
D) H₂SO₄ + BaCl₂ → BaSO₄ + 2HCl
E) CH₃COOH + NaOH → CH₃COONa + H₂O
3. What occurs during oxidation?
A) Gain of protons
B) Gain of electrons
C) Loss of electrons
D) Loss of neutrons
E) Increase in mass
4. Which of the following reactions is not a redox reaction?
A) H₂ + Cl₂ → 2HCl
B) Na + H₂O → NaOH + H₂
C) CuSO₄ + Zn → ZnSO₄ + Cu
D) NaOH + HNO₃ → NaNO₃ + H₂O
E) Fe + CuSO₄ → FeSO₄ + Cu
5. Which element is oxidized in the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu?
A) Cu
B) Zn²⁺
C) Zn
D) H
E) Cu²⁺
6. Which of the following involves both oxidation and reduction?
A) Boiling water
B) Freezing alcohol
C) Burning magnesium
D) Dissolving sugar in water
E) Mixing two gases
7. In the reaction: 2Mg + O₂ → 2MgO, oxygen is:
A) Oxidized
B) Reduced
C) Decomposed
D) Unchanged
E) Ionized
8. Which of the following is always involved in a redox reaction?
A) A base
B) A metal
C) A gas
D) Electron transfer
E) Water
9. In a redox reaction, the substance that is reduced:
A) Gains electrons
B) Loses electrons
C) Releases protons
D) Combines with OH⁻
E) Forms a precipitate
10. What is reduced in the reaction: 2Fe²⁺ + Cl₂ → 2Fe³⁺ + 2Cl⁻?
A) Fe²⁺
B) Fe³⁺
C) Cl₂
D) Cl⁻
E) Both Fe and Cl
11. Which is a redox process?
A) Evaporation
B) Electrolysis of water
C) Dissolving salt in water
D) Melting of ice
E) Filtration of sand
12. Combustion reactions are examples of:
A) Decomposition
B) Redox reactions
C) Precipitation
D) Neutralization
E) Isomerization
13. In a redox reaction, the substance that donates electrons is the:
A) Oxidizing agent
B) Reducer
C) Oxide
D) Precipitate
E) Catalyst
14. What happens to the oxidation number of a substance that is oxidized?
A) It decreases
B) It stays the same
C) It becomes zero
D) It increases
E) It becomes negative
15. Which of the following reactions is a redox reaction?
A) AgNO₃ + HCl → AgCl + HNO₃
B) H₂O + CO₂ → H₂CO₃
C) 2H₂ + O₂ → 2H₂O
D) NaOH + H₂SO₄ → NaHSO₄ + H₂O
E) KBr + AgNO₃ → AgBr + KNO₃
16. In the reaction: CH₄ + 2O₂ → CO₂ + 2H₂O, carbon is:
A) Reduced
B) Oxidized
C) Ionized
D) Precipitated
E) Unchanged
17. The formation of rust (Fe₂O₃) is a result of:
A) Neutralization
B) Hydrolysis
C) Redox reaction
D) Sublimation
E) Isomerization
18. Which of the following always increases in oxidation number in a redox reaction?
A) The oxidizing agent
B) The reduced substance
C) The oxidized substance
D) The product
E) The acid
19. Which reaction is a redox reaction involving chlorine?
A) HCl + NaOH → NaCl + H₂O
B) Cl₂ + 2NaBr → 2NaCl + Br₂
C) NaCl + AgNO₃ → AgCl + NaNO₃
D) Cl⁻ + Ag⁺ → AgCl
E) Cl₂ + H₂O → HClO + HCl
20. What kind of reaction is: Cu + 2AgNO₃ → 2Ag + Cu(NO₃)₂?
A) Precipitation
B) Neutralization
C) Combustion
D) Displacement (Redox)
E) Polymerization
Answers and Explanations
1. C – Redox reactions involve changes in oxidation states due to electron transfer.
2. C – Zn is oxidized and Cu²⁺ is reduced – classic redox.
3. C – Oxidation is defined as loss of electrons.
4. D – NaOH + HNO₃ is a neutralization, not redox (no oxidation number change).
5. C – Zn goes from 0 to +2, hence it is oxidized.
6. C – Burning magnesium involves oxidation of Mg, and reduction of O₂.
7. B – O₂ gains electrons and forms O²⁻ → reduced.
8. D – All redox reactions involve electron transfer.
9. A – Reduction = gain of electrons.
10. C – Cl₂ is reduced to Cl⁻ (0 to –1).
11. B – Electrolysis splits H₂O into H₂ and O₂ via electron transfer.
12. B – Combustion involves oxidation of fuel (C or H).
13. B – The reducer donates electrons and is itself oxidized.
14. D – Oxidized substances have an increase in oxidation number.
15. C – 2H₂ + O₂ → 2H₂O involves oxidation of H₂ and reduction of O₂.
16. B – Carbon in CH₄ goes from –4 to +4 in CO₂ → oxidized.
17. C – Rusting is oxidation of Fe → redox reaction.
18. C – The oxidized species loses electrons → oxidation number increases.
19. B – Cl₂ is reduced (0 to –1), Br⁻ is oxidized (–1 to 0).
20. D – A metal (Cu) replaces Ag⁺ → classic displacement redox reaction.
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