Definition
Oxidation, reduction, redox
Oxidation = loss of electrons / gain of O or loss of H. Reduction = gain of electrons / loss of O or gain of H. Redox = both happen simultaneously.
-- NCERT Class 11 Chemistry, Ch. 7, p. 236Oxidation Reduction Electronic
8 MCQs9-step worked example
Source: NCERT Redox Reactions and ElectrochemistryPYQ coverage: NEET 2021, 2024Official key: NTA-verifiedLast updated: 24 Sep 2026
Oxidation Reduction Electronic, explained for NEET
The electronic concept of oxidation and reduction redefines these classical ideas in terms of electron transfer — and getting the direction wrong is a quiet mark-loser.
The core idea (NCERT Class 11 Chemistry, Chapter 7, page 237): Oxidation is the loss of electrons by a species. Reduction is the gain of electrons. The two always occur together — you cannot have one without the other. This is why the combined process is called a redox reaction.
A species that loses electrons is oxidised and acts as a reducing agent (it causes reduction in something else). A species that gains electrons is reduced and acts as an oxidising agent. The terminology is deliberately inverse: the oxidising agent itself gets reduced.
Where aspirants lose marks: confusing the agent label with the process. When a question asks "identify the reducing agent," many students pick the species that gets reduced — the exact opposite. The rule is mechanical: the reducing agent is the one that donates electrons (gets oxidised). The oxidising agent is the one that accepts electrons (gets reduced).
Consider the reaction: Zn + Cu²⁺ → Zn²⁺ + Cu. Zinc loses 2 electrons (oxidised → reducing agent). Cu²⁺ gains 2 electrons (reduced → oxidising agent). No ambiguity once you track the electron flow.
NEET relevance: Questions on electronic concepts of oxidation and reduction typically appear as recall or conceptual-application items — identify the oxidising/reducing agent, determine which species is oxidised/reduced, or recognise electron transfer in a given reaction. The skill tested is definitional precision, not calculation.
Watch-out: Half-reaction notation makes the electron direction explicit. Always write the half-reactions if the full equation feels ambiguous. Oxidation half: species → species⁺ⁿ + ne⁻. Reduction half: species⁺ⁿ + ne⁻ → species.
Can you answer these Oxidation Reduction Electronic MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
In the electronic concept of redox reactions, oxidation is defined as:
Show answer and why every option is right or wrong
Answer: C. Oxidation is defined as the loss of electrons by a species (NCERT Class 11 Chemistry, Chapter 7, page 237). This is the electronic (modern) definition that supersedes the classical oxygen-based definition.
Why A is wrong: A describes reduction, not oxidation — reduction is the gain of electrons. Confusing the two is the most direct definitional error.
Why B is wrong: B is the classical (oxygen-based) definition of oxidation, not the electronic concept. The question specifically asks about the electronic definition.
Why D is wrong: D is the hydrogen-based classical definition. While historically valid, it is not the electronic concept of oxidation.
MCQ 2Easy RecallPractice
A species that donates electrons in a redox reaction is called:
Show answer and why every option is right or wrong
Answer: B. A species that donates (loses) electrons is the reducing agent — it causes reduction of the other species while itself getting oxidised (NCERT Class 11 Chemistry, Chapter 7, page 237).
Why A is wrong: A is the inverse error — the oxidising agent accepts electrons, not donates them. This agent-label confusion is a common mark-loser.
Why C is wrong: C is a description of what the species becomes (oxidised product), not its role as an agent. The reducing agent becomes the oxidised product, but 'reducing agent' is the correct label for the electron donor.
Why D is wrong: D is incorrect — the reduced product is what the oxidising agent becomes after gaining electrons, not what the electron donor is called.
MCQ 3Easy RecallPractice
In the reaction Fe₂O₃ + 3CO → 2Fe + 3CO₂, which species is reduced?
Show answer and why every option is right or wrong
Answer: B. Fe in Fe₂O₃ is in the +3 oxidation state and gains electrons to become Fe(0). Gain of electrons is reduction (NCERT Class 11 Chemistry, Chapter 7, page 237). Fe₂O₃ (containing Fe³⁺) is the species being reduced.
Why A is wrong: A — CO is oxidised (C goes from +2 in CO to +4 in CO₂), losing electrons. It acts as the reducing agent, not the reduced species.
Why C is wrong: C — CO₂ is a product, not a reactant undergoing change. The question asks which species is reduced, meaning which reactant gains electrons.
Why D is wrong: D — Fe (product) is the result of reduction, not the species being reduced. The question asks about the species undergoing the process, which is Fe³⁺ in Fe₂O₃.
MCQ 4Direct ApplicationPractice
In the reaction 2Na + Cl₂ → 2NaCl, identify the oxidising agent.
Show answer and why every option is right or wrong
Answer: A. Cl₂ accepts electrons (each Cl goes from 0 to −1) and is therefore reduced. The species that gets reduced is the oxidising agent (NCERT Class 11 Chemistry, Chapter 7, page 237).
Why B is wrong: B — NaCl is the product. Agents are identified among the reactants undergoing electron transfer, not among products.
Why C is wrong: C — Na loses an electron (0 → +1), so Na is oxidised. The oxidised species is the reducing agent, not the oxidising agent. This is the classic agent-label inversion error.
Why D is wrong: D — Na⁺ is the oxidised form of sodium in the product. It is not a reactant and cannot be labelled as an agent.
MCQ 5Direct ApplicationPractice
In the half-reaction Mg → Mg²⁺ + 2e⁻, magnesium is:
Show answer and why every option is right or wrong
Answer: D. Mg loses 2 electrons (shown explicitly by the + 2e⁻ on the product side), so it is oxidised. A species that gets oxidised acts as a reducing agent — it donates electrons that reduce something else (NCERT Class 11 Chemistry, Chapter 7, page 237).
Why A is wrong: A — Both labels are wrong. Mg loses electrons (oxidised, not reduced), and the species that is oxidised is a reducing agent, not an oxidising agent.
Why B is wrong: B — Mg is correctly identified as oxidised, but the agent label is inverted. An oxidised species is a reducing agent, not an oxidising agent. This partial-correct option tests whether you can pair process with agent correctly.
Why C is wrong: C — Both labels are wrong. Mg is not reduced (it loses electrons), and therefore it is not acting in the role described.
MCQ 6Direct ApplicationPractice
In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, the reducing agent is:
Show answer and why every option is right or wrong
Answer: A. Zn loses 2 electrons (Zn → Zn²⁺ + 2e⁻) and is oxidised. The species that is oxidised is the reducing agent (NCERT Class 11 Chemistry, Chapter 7, page 237). Zn donates electrons to Cu²⁺.
Why B is wrong: B — SO₄²⁻ is a spectator ion in this reaction. It does not undergo any change in oxidation state and plays no role in the redox process.
Why C is wrong: C — Cu²⁺ gains electrons (Cu²⁺ + 2e⁻ → Cu) and is reduced. The reduced species is the oxidising agent, not the reducing agent.
Why D is wrong: D — Cu is the product formed after Cu²⁺ is reduced. Products are not labelled as agents; agents are identified among the reactants.
MCQ 7Concept TrapPractice
A student claims: "In every redox reaction, the oxidising agent is oxidised." This statement is:
Show answer and why every option is right or wrong
Answer: D. The oxidising agent accepts electrons and is therefore reduced (NCERT Class 11 Chemistry, Chapter 7, page 237). The student's claim inverts the definition. The reducing agent is the one that is oxidised.
Why A is wrong: A — This is the definitional inversion the question tests. The oxidising agent causes oxidation in another species, but itself undergoes reduction (gains electrons).
Why B is wrong: B — The oxidising agent definitely participates in electron transfer — it gains electrons and is reduced. Saying it is 'neither' contradicts the definition of a redox reaction.
Why C is wrong: C — The two agents undergo opposite processes: the oxidising agent is reduced and the reducing agent is oxidised. They do not undergo the same process.
MCQ 8Concept TrapPractice
Consider the reaction: 2H₂ + O₂ → 2H₂O. Which statement correctly identifies both the electronic change AND the agent role?
Show answer and why every option is right or wrong
Answer: C. Each H atom goes from 0 in H₂ to +1 in H₂O — hydrogen loses electrons and is therefore oxidised. The species that is oxidised serves as the reducing agent (NCERT Class 11 Chemistry, Chapter 7, page 237). O₂ gains electrons (0 → −2), making it the oxidising agent.
Why A is wrong: A — H₂ loses electrons, not gains them (H goes from 0 to +1). Both the electron-transfer direction and the agent label are wrong here.
Why B is wrong: B — O₂ gains electrons (each O goes from 0 to −2), not loses them. O₂ is the oxidising agent, not the reducing agent. Both claims in this option are inverted.
Why D is wrong: D — O₂ gains electrons, not loses them. While O₂ is indeed the oxidising agent (correct label), the electron-transfer direction stated is wrong, making the overall statement incorrect.
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How do you solve a Oxidation Reduction Electronic question? A worked example
- 1
Given
In the reaction: MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
Identify which species is oxidised and which is reduced. Name the oxidising agent and the reducing agent. - 2
Required
(a) The species oxidised and the species reduced.
(b) The oxidising agent and the reducing agent. - 3
Concept
Electronic concept of redox: loss of electrons = oxidation; gain of electrons = reduction. The oxidised species is the reducing agent; the reduced species is the oxidising agent (NCERT Class 11 Chemistry, Chapter 7, page 237).
- 4
Formula
No numerical formula needed. The method is: assign oxidation states → identify which element's oxidation state increases (oxidised) and which decreases (reduced).
- 5
Substitution (Oxidation-state tracking)
• Mn in MnO₂: Mn is +4 (since each O is −2, and 2(−2) + Mn = 0 → Mn = +4).• Mn in MnCl₂: Mn is +2 (since each Cl is −1, and 2(−1) + Mn = 0 → Mn = +2).• Mn goes from +4 → +2: gain of 2 electrons → reduced.• Cl in HCl: Cl is −1.• Cl in Cl₂: Cl is 0.• Cl goes from −1 → 0: loss of 1 electron per Cl atom → oxidised.
- 6
Calculation
Not a numerical problem. The electron-transfer analysis is complete above.
Note: Oxidation states like +4, +2, −1, 0 are exact integers (counting the formal charge assignment); they do not involve significant-figure considerations. - 7
Final answer
• Oxidised species: Cl⁻ (in HCl), going from −1 to 0.• Reduced species: Mn⁴⁺ (in MnO₂), going from +4 to +2.• Reducing agent: HCl (contains the Cl⁻ that donates electrons).• Oxidising agent: MnO₂ (contains the Mn⁴⁺ that accepts electrons).
- 8
Common trap
The agent-label inversion: students identify MnO₂ as the reducing agent because Mn "changes more." But the reducing agent is the species that is oxidised (loses electrons) — that is HCl here, not MnO₂. Always ask: "Who lost the electrons?" That species is the reducing agent.
- 9
Similar NEET-style question
In the reaction: 2FeCl₃ + H₂S → 2FeCl₂ + S + 2HCl, identify the oxidising and reducing agents.
(Answer: Fe³⁺ in FeCl₃ is reduced → oxidising agent. S²⁻ in H₂S is oxidised → reducing agent.)
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What to remember before solving Oxidation Reduction Electronic questions
Key Fact
Types of redox reactions
Combination (2 substances → 1), decomposition (1 → ≥2), displacement (active element displaces less active from compound), disproportionation (same element both oxidised and reduced).
-- NCERT Class 11 Chemistry, Ch. 7, p. 242More in Redox Reactions and Electrochemistry: 4 exam traps and mistakes · 5 formulas · 2 question patterns from its other lessons.
Oxidation Reduction Electronic questions from past NEET papers
2 questions from NEET 2021, 2024. Answers verified against NTA official keys.
NEET 2024Revised key
Which reaction is NOT a redox reaction?
1Zn + CuSO₄ → ZnSO₄ + Cu
22KClO₃ + I₂ → 2KIO₃ + Cl₂
3H₂ + Cl₂ → 2HCl
4BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
NTA Answer: Option 4(revised_final)
NEET 2021
Which of the following reactions is the metal displacement reaction? Choose the right option.
12Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂↑
22KClO₃ —[Δ]→ 2KCl + 3O₂
3Cr₂O₃ + 2Al —[Δ]→ Al₂O₃ + 2Cr
4Fe + 2HCl → FeCl₂ + H₂↑
NTA Answer: Option 3(final)
All 21 past-paper questions from Redox Reactions and Electrochemistry →
Sources
NCERT refs: Class 11 Chemistry Chapter 7, p.237
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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