20 MCQs on Oxidation–Reduction (Redox Biology + Basics)

I’ll keep a mix of basics + biological + tricky statement-based questions. Answers are given at the end.

📝 20 MCQs on Oxidation–Reduction (Redox Biology + Basics)

Q1. Which of the following best defines oxidation?

a) Gain of electrons

b) Loss of electrons

c) Gain of hydrogen

d) Loss of oxygen

Q2. Which of the following is true for reduction?

a) Loss of hydrogen

b) Gain of oxygen

c) Gain of hydrogen or electrons

d) Loss of electrons

Q3. The conversion Fe²⁺ → Fe³⁺ represents:

a) Oxidation

b) Reduction

c) Hydrolysis

d) Isomerization

Q4. The conversion Cu²⁺ → Cu⁰ represents:

a) Oxidation

b) Reduction

c) Neutralization

d) Hydroxylation

Q5. Cellular respiration involves:

a) Only reduction

b) Only oxidation

c) Both oxidation and reduction

d) Neutralization

Q6. In photosynthesis, the conversion of CO₂ → Glucose is:

a) Oxidation

b) Reduction

c) Hydrolysis

d) Photophosphorylation

Q7. Conversion of NAD⁺ → NADH is an example of:

a) Oxidation

b) Reduction

c) Hydrolysis

d) Decarboxylation

Q8. Conversion of FADH₂ → FAD is:

a) Reduction

b) Oxidation

c) Hydrolysis

d) Isomerization

Q9. The reaction Cl₂ → 2Cl⁻ is:

a) Oxidation

b) Reduction

c) Photolysis

d) Hydrolysis

Q10. An oxidizing agent is a substance that:

a) Gets oxidized itself

b) Donates electrons

c) Gets reduced and oxidizes another species

d) Releases hydrogen

Q11. A reducing agent is a substance that:

a) Accepts electrons

b) Gets reduced

c) Gets oxidized and reduces another species

d) Donates oxygen

Q12. In cellular respiration, the final electron acceptor is:

a) Glucose

b) Oxygen

c) NADH

d) ATP

Q13. During photolysis of water in photosynthesis, H₂O undergoes:

a) Reduction

b) Oxidation

c) Neutralization

d) Hydrolysis

Q14. Alcohol → Aldehyde conversion is an example of:

a) Reduction

b) Oxidation

c) Hydrolysis

d) Polymerization

Q15. Hydrogen peroxide (H₂O₂) can act as:

a) Only an oxidizing agent

b) Only a reducing agent

c) Both oxidizing and reducing agent

d) Neutral reagent

Q16. Oxidation–Reduction reactions are always:

a) Independent reactions

b) Coupled reactions

c) Neutralization reactions

d) Hydrolysis reactions

Q17. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, the species oxidized is:

a) Zn

b) Cu²⁺

c) Cu

d) Both Zn and Cu²

Q18. In the same reaction Zn + Cu²⁺ → Zn²⁺ + Cu, the species reduced is:

a) Zn

b) Cu²⁺

c) Zn²⁺

d) O₂

Q19. The electron transport chain (ETC) in mitochondria operates as:

a) Only oxidation steps

b) Only reduction steps

c) A continuous series of coupled redox reactions

d) Hydrolysis reactions

Q20. Addition of an oxygen atom to a compound is generally considered:

a) Oxidation

b) Reduction

c) Neutralization

d) Hydrolysis

✅ Answer Key

1 → b

2 → c

3 → a

4 → b

5 → c

6 → b

7 → b

8 → b

9 → b

10 → c

11 → c

12 → b

13 → b

14 → b

15 → c

16 → b

17 → a

18 → b

19 → c

20 → a