Redox concepts oxidation numbers and balancing redox reactions - Question Bank

1. What is the oxidation state of oxygen in OF₂?
A) -1
B) -2
C) +2
D) +1
2. Which element is reduced when H₂S reacts with Br₂ to form HBr and S?
A) H
B) S
C) Br
D) None
3. In the reaction 3NO₂ + H₂O → 2HNO₃ + NO, what is the oxidation state of nitrogen in NO?
A) +2
B) +4
C) +5
D) 0
4. What is the oxidation state of chlorine in ClF₃?
A) +3
B) +1
C) -1
D) +5
5. Balance the reaction: P₄ + OH⁻ → PH₃ + PO₄³⁻ (in basic medium). What is the coefficient of P₄?
A) 1
B) 2
C) 3
D) 4
6. Which of the following is a strong oxidizing agent?
A) SO₂
B) H₂S
C) KMnO₄
D) CO
7. What is the oxidation number of carbon in C₆H₁₂O₆ (glucose)?
A) 0
B) +1
C) -1
D) +2
8. In the reaction 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 5Cl₂ + 8H₂O, what is oxidized?
A) K
B) Mn
C) Cl (in HCl)
D) H
9. What is the oxidation state of sulfur in Na₂S₂O₃ (sodium thiosulfate)?
A) +2
B) +2.5
C) +4
D) +6
10. Balance the following redox reaction in basic medium: Ni(OH)₂ + N₂O₄ → Ni₂O₃ + NO₂⁻ + H₂O. What is the coefficient of N₂O₄?
A) 1
B) 2
C) 3
D) 4
11. Which of the following is the most likely oxidation state of iodine in IF₅?
A) +1
B) +3
C) +5
D) -1
12. What is the oxidation number of phosphorus in PCl₃?
A) +3
B) +5
C) -3
D) 0
13. Which species is reduced in the reaction: 5H₂O₂ + 2MnO₄⁻ + 6H⁺ → 5O₂ + 2Mn²⁺ + 8H₂O?
A) H₂O₂
B) MnO₄⁻
C) H⁺
D) O₂
14. What is the oxidation state of carbon in CH₄?
A) +4
B) -4
C) 0
D) +2
15. Balance the reaction: C₂O₄²⁻ + MnO₄⁻ → CO₂ + Mn²⁺ (in acidic medium). What is the coefficient of MnO₄⁻?
A) 1
B) 2
C) 3
D) 5
16. In the Haber process (N₂ + 3H₂ ⇌ 2NH₃), what is the oxidation state of nitrogen in NH₃?
A) 0
B) +1
C) -3
D) +3
17. What is the oxidation number of oxygen in O₂F₂?
A) -1
B) -2
C) +1
D) +2
18. Which of the following is an example of a disproportionation reaction?
A) Zn + CuSO₄ → ZnSO₄ + Cu
B) 2H₂O₂ → 2H₂O + O₂
C) HCl + NaOH → NaCl + H₂O
D) Fe + S → FeS
19. What is the oxidation state of sulfur in H₂S₂O₇ (oleum)?
A) +4
B) +5
C) +6
D) -2
20. Balance the reaction: BrO₃⁻ + Br⁻ → Br₂ (in acidic medium). What is the coefficient of BrO₃⁻?
A) 1
B) 2
C) 3
D) 4
21. What is the oxidation state of iron in Fe₃O₄?
A) +2
B) +3
C) +8/3
D) +4
22. In the reaction: 2KClO₃ → 2KCl + 3O₂, what is oxidized?
A) K
B) Cl
C) O
D) None
23. What is the oxidation number of nitrogen in N₂O₅?
A) +5
B) +2
C) +1
D) 0
24. Identify the reducing agent in the reaction: I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻
A) I₂
B) S₂O₃²⁻
C) I⁻
D) S₄O₆²⁻
25. What is the oxidation state of phosphorus in H₃PO₄?
A) +3
B) +5
C) +1
D) -3
26. Balance the following redox reaction in basic medium: ClO⁻ + Cr(OH)₃ → Cl⁻ + CrO₄²⁻. What is the coefficient of Cr(OH)₃?
A) 1
B) 2
C) 3
D) 4
27. In a redox reaction, the substance that loses electrons is said to be:
A) Oxidized
B) Reduced
C) Catalyzed
D) Neutralized
28. What is the oxidation number of sulfur in S₈?
A) 0
B) +1
C) -1
D) +2
29. Which element is reduced in the reaction: 2Na + Cl₂ → 2NaCl?
A) Na
B) Cl
C) Both
D) Neither
30. What is the oxidation state of chlorine in NaClO₃?
A) +1
B) +3
C) +5
D) -1
31. Balance the reaction: MnO₄⁻ + S²⁻ → Mn²⁺ + S (in acidic medium). What is the coefficient of S²⁻?
A) 1
B) 2
C) 3
D) 5
32. What is the oxidation number of chromium in CrO₅?
A) +5
B) +6
C) +8
D) +10
33. Which of the following is a characteristic of a reducing agent?
A) It causes oxidation
B) It gains electrons
C) Its oxidation number decreases
D) It is always reduced
34. In which of the following compounds does manganese exhibit its highest oxidation state?
A) MnO₂
B) KMnO₄
C) Mn₂O₃
D) MnO
35. What is the oxidation state of carbon in CO₂?
A) 0
B) +2
C) +4
D) -4
36. Balance the following redox reaction in acidic medium: Cr₂O₇²⁻ + SO₂ → Cr³⁺ + SO₄²⁻. What is the coefficient of SO₂?
A) 1
B) 2
C) 3
D) 4
37. The process of gaining electrons is known as:
A) Oxidation
B) Reduction
C) Disproportionation
D) Combustion
38. What is the oxidation number of oxygen in H₂O₂?
A) -1
B) -2
C) 0
D) +1
39. Which species acts as a reducing agent in the reaction: 2KMnO₄ + 10FeSO₄ + 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 8H₂O?
A) KMnO₄
B) FeSO₄
C) H₂SO₄
D) Fe₂(SO₄)₃
40. What is the oxidation state of nitrogen in NH₃?
A) +3
B) -3
C) 0
D) +1
41. In the reaction 2H₂S + SO₂ → 3S + 2H₂O, what is oxidized?
A) H₂S
B) SO₂
C) S
D) H₂O
42. What is the sum of oxidation numbers of all atoms in K₂Cr₂O₇?
A) 0
B) +1
C) +2
D) +6
43. Which of the following is not a redox reaction?
A) Combustion of methane
B) Neutralization of HCl by NaOH
C) Rusting of iron
D) Electrolysis of water
44. What is the oxidation state of phosphorus in P₄O₁₀?
A) +2
B) +4
C) +5
D) -3
45. In a redox reaction, the substance that gains electrons is said to be:
A) Oxidized
B) Reduced
C) Catalyzed
D) Neutralized
46. What is the oxidation number of chlorine in HClO₄?
A) +1
B) +3
C) +5
D) +7
47. Identify the oxidizing agent in the reaction: 5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O
A) Fe²⁺
B) MnO₄⁻
C) H⁺
D) Fe³⁺
48. What is the oxidation state of manganese in KMnO₄?
A) +2
B) +4
C) +6
D) +7
49. Which element is oxidized in the reaction: Zn + CuSO₄ → ZnSO₄ + Cu?
A) Zn
B) Cu
C) S
D) O
50. In the reaction 2Na + Cl₂ → 2NaCl, what is the oxidation state of sodium in NaCl?
A) 0
B) +1
C) -1
D) +2
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