1. Oxidation is defined as:
A) Gain of electrons
B) Loss of electrons
C) Gain of protons
D) Loss of neutrons
Answer: B
Explanation: Oxidation is the process in which an atom, ion, or molecule loses electrons.
2. Reduction is defined as:
A) Gain of electrons
B) Loss of electrons
C) Gain of protons
D) Loss of neutrons
Answer: A
Explanation: Reduction involves the gain of electrons.
3. In the reaction 
, sodium is:
A) Oxidized
B) Reduced
C) Both oxidized and reduced
D) Neither
Answer: A
Explanation: Sodium loses an electron → oxidation.
4. In the reaction , chlorine is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: B
Explanation: Chlorine gains an electron → reduction.
5. An oxidizing agent:
A) Gains electrons
B) Loses electrons
C) Both
D) None
Answer: A
Explanation: Oxidizing agents oxidize other substances and are themselves reduced (gain electrons).
6. A reducing agent:
A) Gains electrons
B) Loses electrons
C) Both
D) None
Answer: B
Explanation: Reducing agents reduce other substances and are themselves oxidized (lose electrons).
7. The oxidation number of oxygen in H₂O₂ is:
A) -2
B) -1
C) 0
D) +1
Answer: B
Explanation: In peroxide (H₂O₂), oxygen has oxidation number -1.
8. The oxidation number of hydrogen in NaH is:
A) +1
B) 0
C) -1
D) +2
Answer: C
Explanation: In hydrides (NaH), hydrogen is -1.
9. Oxidation involves:
A) Increase in oxidation number
B) Decrease in oxidation number
C) No change in oxidation number
D) Variable
Answer: A
Explanation: Losing electrons increases the oxidation number.
10. Reduction involves:
A) Increase in oxidation number
B) Decrease in oxidation number
C) No change
D) Variable
Answer: B
Explanation: Gaining electrons decreases the oxidation number.
11. In 
, Fe is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: B
Explanation: Fe³⁺ in Fe₂O₃ gains electrons → reduction.
12. In the same reaction, CO is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: A
Explanation: CO loses electrons → oxidation to CO₂.
13. In 
, oxygen is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: B
Explanation: Oxygen gains electrons → reduction.
14. In , hydrogen is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: A
Explanation: Hydrogen loses electrons → oxidation.
15. Oxidation number of sulfur in H₂SO₄ is:
A) +4
B) +6
C) +2
D) -2
Answer: B
Explanation: Calculation: 2(H⁺) + S + 4(O²⁻) = 0 → S = +6.
16. Oxidation number of nitrogen in NH₄⁺ is:
A) -3
B) +1
C) 0
D) +5
Answer: A
Explanation: H⁺ = +1, sum of charges = +1 → N = -3.
17. Oxidation number of Cl in ClO₄⁻ is:
A) +7
B) +5
C) +3
D) +1
Answer: A
Explanation: O = -2, 4×(-2) + Cl = -1 → Cl = +7.
18. In 
, Zn is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: A
Explanation: Zn loses 2 electrons → oxidized.
19. In the same reaction, Cu²⁺ is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: B
Explanation: Cu²⁺ gains 2 electrons → reduced.
20. Which of the following is a good oxidizing agent?
A) KMnO₄
B) H₂
C) Zn
D) Na
Answer: A
Explanation: KMnO₄ in acidic medium accepts electrons → oxidizes other substances.
21. Which of the following is a good reducing agent?
A) NaBH₄
B) O₂
C) H₂O₂
D) KMnO₄
Answer: A
Explanation: NaBH₄ donates electrons → reduces other substances.
22. Oxidation number of carbon in CO₂ is:
A) +2
B) +4
C) -2
D) 0
Answer: B
Explanation: O = -2, 2×(-2) + C = 0 → C = +4.
23. Oxidation number of carbon in CH₄ is:
A) +4
B) -4
C) 0
D) +2
Answer: B
Explanation: H = +1, 4×(+1) + C = 0 → C = -4.
24. In disproportionation reactions:
A) Same species is both oxidized and reduced
B) Two different species react
C) Only oxidation occurs
D) Only reduction occurs
Answer: A
Explanation: E.g., 
, O in H₂O₂ is both reduced and oxidized.
25. Which element can show disproportionation?
A) Chlorine in hypochlorite solution
B) Sodium
C) Magnesium
D) Helium
Answer: A
Explanation: Cl in NaOCl is partially oxidized to ClO₃⁻ and partially reduced to Cl⁻.
26. In the reaction 
, the number of electrons transferred per Fe atom is:
A) 1
B) 2
C) 3
D) 0
Answer: B
Explanation: Fe → Fe²⁺ + 2e⁻, so 2 electrons are transferred per atom.
27. Oxidation number change in 
for Mn is:
A) +7 → +2
B) +2 → +7
C) +6 → +2
D) +7 → +6
Answer: A
Explanation: Mn goes from +7 in MnO₄⁻ to +2 in Mn²⁺ → gain of 5 electrons.
28. In the same reaction, Fe²⁺ is:
A) Oxidized to Fe³⁺
B) Reduced to Fe⁰
C) Both
D) Neither
Answer: A
Explanation: Fe²⁺ loses one electron → Fe³⁺ → oxidized.
29. Redox reaction is a reaction where:
A) Only oxidation occurs
B) Only reduction occurs
C) Both oxidation and reduction occur simultaneously
D) No electron transfer occurs
Answer: C
Explanation: A redox reaction involves simultaneous oxidation and reduction.
30. Which of the following is an example of a redox reaction?
A) Zn + 2HCl → ZnCl₂ + H₂
B) HCl + NaOH → NaCl + H₂O
C) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
D) AgNO₃ + NaCl → AgCl + NaNO₃
Answer: A
Explanation: Zn → Zn²⁺ (oxidation), H⁺ → H₂ (reduction).
31. In balancing redox reactions by oxidation number method, first step is:
A) Identify oxidizing and reducing agents
B) Balance all atoms except H and O
C) Balance electrons lost and gained
D) Multiply to equalize electrons
Answer: A
Explanation: First step is to identify which species are oxidized and reduced.
32. In acidic medium, H₂O is used to:
A) Balance H atoms
B) Balance O atoms
C) Balance electrons
D) None
Answer: B
Explanation: Water is added to balance oxygen atoms in acidic medium.
33. In basic medium, OH⁻ is used to:
A) Balance O atoms
B) Balance H atoms
C) Balance electrons
D) Both A & B
Answer: D
Explanation: OH⁻ balances H and O in basic medium reactions.
34. The number of electrons transferred in 
is:
A) 3
B) 6
C) 2
D) 4
Answer: B
Explanation: Cr → Cr³⁺ loses 3e⁻ per atom, 2 atoms → 6 electrons.
35. Oxidation number of Cr in Cr₂O₇²⁻ is:
A) +3
B) +6
C) +4
D) +2
Answer: B
Explanation: O = -2, 7×(-2) + 2×Cr = -2 → Cr = +6.
36. In the reaction 
, Cl is:
A) Both oxidized and reduced
B) Only oxidized
C) Only reduced
D) Neither
Answer: A
Explanation: Disproportionation: Cl in Cl₂ (0) → Cl⁻ (-1, reduced) and Cl⁺ (+1 in ClO⁻, oxidized).
37. Strongest oxidizing agent in acidic medium:
A) KMnO₄
B) Na₂SO₄
C) NaCl
D) H₂O
Answer: A
Explanation: KMnO₄ has Mn⁷⁺ → easily reduced → strong oxidizing agent.
38. Strongest reducing agent among: H₂, Na, CO, C
Answer: Na
Explanation: Sodium readily loses electron → strong reducing agent.
39. Standard electrode potential (E°) measures:
A) Oxidizing power
B) Reducing power
C) Both
D) Neither
Answer: A
Explanation: Positive E° → good oxidizing agent; negative E° → good reducing agent.
40. Which metal can displace Zn from ZnSO₄ solution?
A) Cu
B) Mg
C) Ag
D) Au
Answer: B
Explanation: Mg is more reactive (higher in electrochemical series) → displaces Zn²⁺.
41. Electrochemical series arranges elements according to:
A) Atomic number
B) Electronegativity
C) Standard reduction potential
D) Density
Answer: C
Explanation: Electrochemical series ranks elements by standard reduction potential (E°).
42. In the reaction 
, Cl₂ is:
A) Oxidizing agent
B) Reducing agent
C) Both
D) Neither
Answer: A
Explanation: Cl₂ gains electrons → reduced, acts as oxidizing agent.
43. In 
, Cu is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: A
Explanation: Cu → Cu²⁺ loses 2 electrons → oxidation.
44. In the same reaction, Ag⁺ is:
A) Oxidized
B) Reduced
C) Both
D) Neither
Answer: B
Explanation: Ag⁺ gains electrons → reduction.
45. In corrosion of iron, Fe reacts with O₂ and H₂O to form:
A) FeO
B) Fe₂O₃·xH₂O
C) FeCl₃
D) FeS
Answer: B
Explanation: Rust is hydrated ferric oxide → Fe₂O₃·xH₂O.
46. Redox titration uses:
A) KMnO₄ and oxalic acid
B) HCl and NaOH
C) BaCl₂ and Na₂SO₄
D) NaCl and AgNO₃
Answer: A
Explanation: KMnO₄ oxidizes oxalic acid in redox titration.
47. In 
, H₂O₂ acts as:
A) Oxidizing agent
B) Reducing agent
C) Both
D) Neither
Answer: C
Explanation: H₂O₂ disproportionates → gets oxidized and reduced simultaneously.
48. Disproportionation of Cl₂ in water forms:
A) HCl and HClO
B) HCl only
C) HClO only
D) Cl₂O
Answer: A
Explanation: Cl₂ + H₂O → HCl + HClO.
49. Oxidation number of Mn in MnO₄²⁻ is:
A) +6
B) +7
C) +4
D) +2
Answer: A
Explanation: Mn + 4(-2) = -2 → Mn = +6.
50. The reducing agent in 
is:
A) Zn
B) H⁺
C) Cl⁻
D) H₂
Answer: A
Explanation: Zn loses electrons → reduces H⁺ to H₂ → Zn is reducing agent.
51. Electrolysis is:
A) A redox reaction occurring spontaneously
B) Non-spontaneous redox reaction driven by electricity
C) Oxidation only
D) Reduction only
Answer: B
Explanation: Electrolysis uses external electrical energy to drive non-spontaneous redox reactions.
52. In electrolysis, the electrode where oxidation occurs is called:
A) Cathode
B) Anode
C) Electrolyte
D) Salt bridge
Answer: B
Explanation: Oxidation occurs at the anode (positive in electrolysis).
53. In electrolysis, the electrode where reduction occurs is called:
A) Cathode
B) Anode
C) Electrolyte
D) Salt bridge
Answer: A
Explanation: Reduction occurs at the cathode (negative in electrolysis).
54. During electrolysis of molten NaCl, the products at cathode and anode are:
A) Na at cathode, Cl₂ at anode
B) Cl₂ at cathode, Na at anode
C) NaCl at cathode, Na at anode
D) Na at both electrodes
Answer: A
Explanation: Na⁺ reduced at cathode → Na; Cl⁻ oxidized at anode → Cl₂.
55. In aqueous electrolysis, water can compete with ions because:
A) Water is inert
B) Water can also be oxidized/reduced
C) Water is a good conductor
D) None
Answer: B
Explanation: H₂O can be reduced to H₂ or oxidized to O₂ depending on ion reduction potential.
56. In electrolysis of CuSO₄ with copper electrodes, the cathode:
A) Loses Cu
B) Gains Cu
C) Loses O₂
D) Gains H₂
Answer: B
Explanation: Cu²⁺ ions are reduced → deposited on cathode.
57. Galvanic cell is:
A) A non-spontaneous redox reaction
B) A spontaneous redox reaction producing electricity
C) Oxidation only
D) Reduction only
Answer: B
Explanation: Galvanic/voltaic cells convert chemical energy into electrical energy spontaneously.
58. In a Daniell cell, the anode reaction is:
A) Zn → Zn²⁺ + 2e⁻
B) Cu²⁺ + 2e⁻ → Cu
C) Cu → Cu²⁺ + 2e⁻
D) Zn²⁺ + 2e⁻ → Zn
Answer: A
Explanation: Zn is oxidized at the anode → Zn²⁺ + 2e⁻.
59. In a Daniell cell, the cathode reaction is:
A) Zn → Zn²⁺ + 2e⁻
B) Cu²⁺ + 2e⁻ → Cu
C) Cu → Cu²⁺ + 2e⁻
D) Zn²⁺ + 2e⁻ → Zn
Answer: B
Explanation: Cu²⁺ ions are reduced at the cathode → Cu metal.
60. The salt bridge in a galvanic cell:
A) Prevents mixing of solutions
B) Maintains electrical neutrality
C) Conducts electrons directly
D) Produces ions
Answer: B
Explanation: Salt bridge allows ion flow to maintain charge balance.
61. Standard electrode potential (E°) is measured under:
A) 1 atm pressure, 25°C, 1 M solution
B) Any condition
C) High temperature only
D) Low pressure only
Answer: A
Explanation: Standard conditions: 25°C, 1 atm, 1 M solution.
62. Element with higher E° is:
A) Stronger reducing agent
B) Stronger oxidizing agent
C) Less reactive
D) Inert
Answer: B
Explanation: Higher E° → greater tendency to gain electrons → strong oxidizing agent.
63. Which metal can reduce Ag⁺ from solution?
A) Zn
B) Cu
C) Hg
D) Au
Answer: A
Explanation: Zn has lower E° → stronger reducing agent than Ag⁺.
64. In electroplating, the object to be plated is:
A) Anode
B) Cathode
C) Electrolyte
D) Salt bridge
Answer: B
Explanation: Object to be plated is cathode → receives metal ions.
65. Electroplating prevents:
A) Oxidation
B) Corrosion
C) Both
D) Neither
Answer: C
Explanation: Coating of metal protects surface from corrosion and oxidation.
66. Lead storage battery is:
A) Primary cell
B) Secondary cell
C) Fuel cell
D) None
Answer: B
Explanation: Lead-acid battery can be recharged → secondary cell.
67. In lead storage battery, the anode during discharge:
A) Pb → PbSO₄ + 2e⁻
B) PbO₂ + 4H⁺ + SO₄²⁻ + 2e⁻ → PbSO₄ + 2H₂O
C) Pb²⁺ + 2e⁻ → Pb
D) None
Answer: A
Explanation: Pb anode oxidized to PbSO₄ during discharge.
68. In lead storage battery, cathode during discharge:
A) Pb → PbSO₄
B) PbO₂ reduced → PbSO₄
C) Pb²⁺ → Pb
D) None
Answer: B
Explanation: PbO₂ reduced → PbSO₄.
69. Dry cell is:
A) Primary cell
B) Secondary cell
C) Fuel cell
D) Electrolytic cell
Answer: A
Explanation: Dry cells are non-rechargeable → primary cells.
70. In molten NaCl electrolysis, Cl⁻ ions migrate to:
A) Cathode
B) Anode
C) Electrolyte
D) Salt bridge
Answer: B
Explanation: Cl⁻ is oxidized at anode → Cl₂ gas.
71. In molten NaCl electrolysis, Na⁺ ions migrate to:
A) Cathode
B) Anode
C) Electrolyte
D) Salt bridge
Answer: A
Explanation: Na⁺ is reduced at cathode → Na metal.
72. The cell in which chemical energy is converted to electrical energy spontaneously is:
A) Galvanic cell
B) Electrolytic cell
C) Fuel cell
D) Dry cell
Answer: A
Explanation: Galvanic cell produces electricity from spontaneous redox reactions.
73. Which of the following can act as both oxidizing and reducing agent?
A) H₂O₂
B) Zn
C) Cu
D) HCl
Answer: A
Explanation: H₂O₂ disproportionates → reduced to H₂O and oxidized to O₂.
74. Oxidizing power of halogens decreases down the group because:
A) Electronegativity decreases
B) Atomic size increases
C) Both A & B
D) None
Answer: C
Explanation: Lower electronegativity and larger size → weaker oxidizing ability.
75. Redox reaction is widely used in:
A) Metal extraction
B) Electroplating
C) Batteries
D) All of these
Answer: D
Explanation: Redox reactions are fundamental in industry, electrochemistry, and energy storage.
76. Corrosion of iron occurs faster in:
A) Dry air
B) Moist air
C) Pure oxygen
D) Pure nitrogen
Answer: B
Explanation: Water acts as an electrolyte → promotes redox reaction → rust formation.
77. The main product of iron corrosion is:
A) FeO
B) Fe₂O₃·xH₂O
C) FeCl₃
D) FeS
Answer: B
Explanation: Rust is hydrated ferric oxide (Fe₂O₃·xH₂O).
78. In corrosion, the anode is:
A) Fe
B) O₂
C) H₂O
D) Fe²⁺
Answer: A
Explanation: Fe loses electrons → oxidation occurs at anodic sites.
79. Cathodic protection prevents corrosion by:
A) Applying electric current
B) Coating with metal like Zn
C) Both A & B
D) Using water
Answer: C
Explanation: Cathodic protection reduces oxidation of Fe → via sacrificial anode or impressed current.
80. In sacrificial protection, the anode is:
A) More reactive metal than iron
B) Less reactive metal than iron
C) Iron itself
D) Non-metal
Answer: A
Explanation: Metal like Zn or Mg corrodes instead of iron → sacrificial protection.
81. In fuel cells, chemical energy is converted into electricity:
A) Spontaneously
B) Non-spontaneously
C) Only with external battery
D) Only at high temperature
Answer: A
Explanation: Fuel cells use spontaneous redox reactions (e.g., H₂ + O₂ → H₂O).
82. In hydrogen fuel cell, the anode reaction is:
A) H₂ → 2H⁺ + 2e⁻
B) O₂ + 4H⁺ + 4e⁻ → 2H₂O
C) H₂ + O₂ → H₂O
D) H⁺ + e⁻ → H
Answer: A
Explanation: Hydrogen is oxidized at anode → electrons flow to cathode.
83. In hydrogen fuel cell, cathode reaction is:
A) H₂ → 2H⁺ + 2e⁻
B) O₂ + 4H⁺ + 4e⁻ → 2H₂O
C) H⁺ + e⁻ → H
D) H₂ + O₂ → H₂O
Answer: B
Explanation: Oxygen is reduced at cathode to form water.
84. Standard potential of SHE (standard hydrogen electrode) is:
A) 0 V
B) +1 V
C) -1 V
D) 0.5 V
Answer: A
Explanation: By definition, standard electrode potential of SHE = 0 V.
85. In organic redox, KMnO₄ oxidizes:
A) Alcohols to aldehydes/carboxylic acids
B) Alkanes to alkenes
C) Aromatics to halides
D) None
Answer: A
Explanation: KMnO₄ is a strong oxidizing agent → oxidizes primary alcohols to carboxylic acids.
86. Oxidation of ethanol with acidified K₂Cr₂O₇ gives:
A) CH₃CHO (acetaldehyde) or CH₃COOH (acetic acid)
B) CH₄
C) C₂H₆
D) C₂H₅Cl
Answer: A
Explanation: Primary alcohol → aldehyde → carboxylic acid on complete oxidation.
87. Redox titration can be done using:
A) KMnO₄
B) Iodine
C) Both A & B
D) NaCl
Answer: C
Explanation: Both KMnO₄ and I₂ are commonly used in redox titrations.
88. Oxidation number of C in HCOOH is:
A) -1
B) +2
C) 0
D) +1
Answer: B
Explanation: H = +1, O = -2, sum = 0 → C = +2.
89. Chlorine water reacts with KI to form:
A) I₂ + HCl
B) Cl₂ + KI
C) HCl + KClO
D) I₂ + KCl + H₂O
Answer: D
Explanation: Cl₂ oxidizes I⁻ → I₂, also forms KCl and H₂O.
90. Oxidation number of nitrogen in HNO₃ is:
A) +5
B) +3
C) +2
D) 0
Answer: A
Explanation: H = +1, 3O = -6, N = +5 to balance charge → HNO₃ neutral.
91. Which metal is used as sacrificial anode for iron protection?
A) Zn
B) Cu
C) Fe
D) Pb
Answer: A
Explanation: Zn is more reactive → corrodes instead of iron.
92. In contact process, SO₂ is oxidized to SO₃ using:
A) V₂O₅
B) H₂SO₄
C) O₂
D) Fe
Answer: A
Explanation: V₂O₅ acts as catalyst for oxidation → redox reaction.
93. In electrorefining of copper, anode is:
A) Impure Cu
B) Pure Cu
C) Graphite
D) Zn
Answer: A
Explanation: Impure Cu oxidized → dissolves as Cu²⁺ → deposited on cathode.
94. Cathode in electrorefining of copper:
A) Impure Cu
B) Pure Cu
C) Graphite
D) Zn
Answer: B
Explanation: Cu²⁺ reduced at cathode → pure Cu metal deposited.
95. In voltaic cell, electrons flow from:
A) Anode → Cathode
B) Cathode → Anode
C) Salt bridge → Cathode
D) Electrolyte → Anode
Answer: A
Explanation: Electrons flow from oxidized species (anode) → reduced species (cathode).
96. Which is strongest oxidizing agent among halogens?
A) F₂
B) Cl₂
C) Br₂
D) I₂
Answer: A
Explanation: Fluorine has highest electronegativity → strongest oxidizing agent.
97. In corrosion, moisture accelerates rusting because:
A) Acts as electrolyte
B) Dissolves CO₂
C) Both A & B
D) None
Answer: C
Explanation: Moisture + CO₂ → weak carbonic acid → accelerates iron oxidation.
98. Redox reactions are important in:
A) Bleaching
B) Disinfection
C) Metallurgy
D) All of these
Answer: D
Explanation: Redox reactions are central in chemical industry, health, and metal extraction.
99. Oxidation number of Cr in K₂Cr₂O₇ is:
A) +6
B) +3
C) +2
D) +4
Answer: A
Explanation: K = +1, O = -2 → Cr = +6.
100. Oxidizing agent in redox reaction is always:
A) Reduced
B) Oxidized
C) Neither
D) Both
Answer: A
Explanation: Oxidizing agent gains electrons → gets reduced.