Redox Reactions MCQs – Class 11 Chemistry
Redox Reactions MCQs – Class 11 Chemistry
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Physical Chemistry – MCQ Titles
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT chapter “Redox Reactions”. The questions are arranged section-wise to ensure complete syllabus coverage and include clear, concept-clearing explanations, making them ideal for CBSE Class 11 board exam preparation.
Section A: Concept of Oxidation and Reduction
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 involves loss of electrons.
2. Reduction is defined as
A. loss of electrons
B. loss of oxygen
C. gain of electrons
D. gain of protons
Answer: C
Explanation: Reduction involves gain of electrons.
3. Oxidation and reduction always occur
A. separately
B. simultaneously
C. alternately
D. independently
Answer: B
Explanation: Oxidation and reduction are complementary processes.
4. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, zinc is
A. reduced
B. oxidised
C. both oxidised and reduced
D. unchanged
Answer: B
Explanation: Zinc loses electrons, hence oxidised.
Section B: Oxidation Number (Oxidation State)
5. Oxidation number of an element in free state is
A. +1
B. −1
C. 0
D. variable
Answer: C
Explanation: Free elements have oxidation number zero.
6. Oxidation number of oxygen in most compounds is
A. −1
B. −2
C. +2
D. 0
Answer: B
Explanation: Oxygen usually has oxidation number −2.
7. Oxidation number of hydrogen in metal hydrides is
A. +1
B. −1
C. 0
D. +2
Answer: B
Explanation: In metal hydrides, hydrogen is −1.
8. Oxidation number of sulphur in H₂SO₄ is
A. +4
B. +6
C. −2
D. +2
Answer: B
Explanation: Total oxidation number must be zero.
9. Oxidation number of chlorine in KClO₃ is
A. −1
B. +1
C. +5
D. +7
Answer: C
Explanation: Chlorine is in +5 oxidation state.
Section C: Redox Reactions in Terms of Oxidation Number
10. A redox reaction involves
A. only oxidation
B. only reduction
C. change in oxidation numbers
D. formation of precipitate
Answer: C
Explanation: Oxidation numbers change during redox reactions.
11. In the reaction Fe²⁺ → Fe³⁺, iron is
A. oxidised
B. reduced
C. unchanged
D. neutralised
Answer: A
Explanation: Oxidation number increases from +2 to +3.
12. In the reaction Cl₂ → 2Cl⁻, chlorine is
A. oxidised
B. reduced
C. neutralised
D. unchanged
Answer: B
Explanation: Chlorine gains electrons.
13. Which of the following is NOT a redox reaction?
A. Zn + CuSO₄ → ZnSO₄ + Cu
B. HCl + NaOH → NaCl + H₂O
C. Fe₂O₃ + 3CO → 2Fe + 3CO₂
D. 2Mg + O₂ → 2MgO
Answer: B
Explanation: Neutralisation reaction without change in oxidation state.
Section D: Oxidising and Reducing Agents
14. An oxidising agent is a substance that
A. gains electrons
B. loses electrons
C. gets oxidised
D. reduces others
Answer: A
Explanation: Oxidising agent itself gets reduced.
15. A reducing agent is a substance that
A. gains electrons
B. loses electrons
C. gets reduced
D. oxidises others
Answer: B
Explanation: Reducing agent donates electrons.
16. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, Cu²⁺ acts as
A. reducing agent
B. oxidising agent
C. catalyst
D. spectator ion
Answer: B
Explanation: Cu²⁺ gains electrons.
17. Which of the following is a strong oxidising agent?
A. Zn
B. H₂
C. KMnO₄
D. Fe
Answer: C
Explanation: KMnO₄ readily accepts electrons.
Section E: Types of Redox Reactions
18. A reaction in which one substance is both oxidised and reduced is called
A. combination reaction
B. disproportionation reaction
C. decomposition reaction
D. displacement reaction
Answer: B
Explanation: Same element undergoes oxidation and reduction.
19. Which is a disproportionation reaction?
A. 2H₂ + O₂ → 2H₂O
B. 2CuO → 2Cu + O₂
C. 2H₂O₂ → 2H₂O + O₂
D. Zn + H₂SO₄ → ZnSO₄ + H₂
Answer: C
Explanation: Oxygen undergoes both oxidation and reduction.
20. A displacement reaction is an example of
A. acid–base reaction
B. redox reaction
C. precipitation reaction
D. neutralisation reaction
Answer: B
Explanation: Oxidation and reduction occur.
Section F: Balancing Redox Reactions
21. Balancing redox reactions is based on
A. law of definite proportions
B. conservation of mass
C. conservation of charge and atoms
D. law of octaves
Answer: C
Explanation: Both charge and atoms must be balanced.
22. The oxidation number method balances reactions by
A. balancing atoms first
B. balancing electrons lost and gained
C. balancing charges only
D. balancing coefficients randomly
Answer: B
Explanation: Total electrons lost equal electrons gained.
23. Which method is commonly used in acidic medium?
A. Half-reaction method
B. Hit and trial
C. Inspection method
D. Valency method
Answer: A
Explanation: Half-reaction method is suitable for ionic reactions.
24. In basic medium, H⁺ ions are balanced by adding
A. H₂O
B. OH⁻
C. O₂
D. H₂
Answer: B
Explanation: OH⁻ neutralises excess H⁺ ions.
Section G: Redox Reactions in Daily Life
25. Rusting of iron is an example of
A. reduction
B. oxidation
C. corrosion (redox process)
D. neutralisation
Answer: C
Explanation: Rusting involves oxidation and reduction.
26. Respiration is a
A. physical process
B. endothermic process
C. redox reaction
D. neutralisation reaction
Answer: C
Explanation: Glucose is oxidised and oxygen is reduced.
27. Photosynthesis is a
A. reduction reaction only
B. oxidation reaction only
C. redox reaction
D. decomposition reaction
Answer: C
Explanation: CO₂ is reduced and water is oxidised.
Section H: Redox Reactions in Electrochemistry
28. In electrochemical cells, oxidation occurs at
A. cathode
B. anode
C. salt bridge
D. electrolyte
Answer: B
Explanation: Oxidation always occurs at anode.
29. Reduction occurs at
A. anode
B. cathode
C. electrolyte
D. salt bridge
Answer: B
Explanation: Reduction always occurs at cathode.
30. Transfer of electrons in redox reactions leads to
A. heat only
B. electrical energy
C. chemical change
D. all of these
Answer: D
Explanation: Electron transfer causes energy and chemical changes.
Section I: Conceptual NCERT-Based MCQs
31. Which species is oxidised in the reaction
2Al + Fe₂O₃ → Al₂O₃ + 2Fe?
A. Iron
B. Oxygen
C. Aluminium
D. Fe₂O₃
Answer: C
Explanation: Aluminium loses electrons.
32. Oxidation number of nitrogen in NH₃ is
A. −3
B. +3
C. +5
D. 0
Answer: A
Explanation: Nitrogen has oxidation state −3.
33. Which element shows maximum number of oxidation states?
A. Carbon
B. Oxygen
C. Iron
D. Manganese
Answer: D
Explanation: Manganese shows oxidation states from +2 to +7.
34. Which reaction involves no change in oxidation state?
A. Combustion
B. Neutralisation
C. Displacement
D. Rusting
Answer: B
Explanation: Acid–base reactions involve proton transfer.
35. Oxidation number of chromium in K₂Cr₂O₇ is
A. +3
B. +6
C. +7
D. +4
Answer: B
Explanation: Chromium is in +6 state.
Section J: Application-Based MCQs
36. Bleaching powder acts as
A. reducing agent
B. oxidising agent
C. catalyst
D. buffer
Answer: B
Explanation: It releases nascent oxygen.
37. Which of the following undergoes oxidation in respiration?
A. Oxygen
B. Carbon dioxide
C. Glucose
D. Water
Answer: C
Explanation: Glucose is oxidised to CO₂.
38. Which substance is both oxidising and reducing agent?
A. H₂SO₄
B. KMnO₄
C. H₂O₂
D. NaCl
Answer: C
Explanation: Hydrogen peroxide shows dual behaviour.
39. In redox reactions, total oxidation number of reactants and products is
A. equal
B. zero
C. positive
D. negative
Answer: A
Explanation: Oxidation number is conserved.
40. Which compound shows disproportionation?
A. H₂O
B. Cl₂ + H₂O
C. NaCl
D. HCl
Answer: B
Explanation: Chlorine undergoes oxidation and reduction.
Section K: Assertion-Based and Conceptual MCQs
41. Increase in oxidation number indicates
A. reduction
B. oxidation
C. neutralisation
D. combination
Answer: B
Explanation: Oxidation number increases on oxidation.
42. Redox reactions involve transfer of
A. atoms
B. protons
C. electrons
D. neutrons
Answer: C
Explanation: Electron transfer defines redox reactions.
43. Which is NOT a redox process?
A. Corrosion
B. Combustion
C. Neutralisation
D. Respiration
Answer: C
Explanation: Neutralisation does not involve electron transfer.
44. Oxidation and reduction can be identified by
A. mass change
B. colour change only
C. electron transfer
D. temperature change
Answer: C
Explanation: Electron transfer is the key feature.
45. In the reaction 2Na + Cl₂ → 2NaCl, sodium is
A. oxidised
B. reduced
C. neutralised
D. unchanged
Answer: A
Explanation: Sodium loses electrons.
46. Which oxidation state of oxygen is found in peroxides?
A. −1
B. −2
C. +2
D. 0
Answer: A
Explanation: Peroxides have O in −1 state.
47. Oxidation number of carbon in CO₂ is
A. +2
B. +4
C. −4
D. 0
Answer: B
Explanation: Carbon is in +4 state.
48. The substance that is oxidised acts as
A. oxidising agent
B. reducing agent
C. catalyst
D. acid
Answer: B
Explanation: It donates electrons.
49. Redox reactions are important in
A. metabolism
B. metallurgy
C. corrosion
D. all of these
Answer: D
Explanation: Redox reactions occur widely in nature and industry.
50. Redox reactions are best explained using
A. atomic mass
B. oxidation number
C. molecular mass
D. density
Answer: B
Explanation: Oxidation numbers track electron transfer.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Redox Reactions, ideal for concept clarity, revision, and board exam preparation.