Free Oxidation and Reduction MCQs with Answers
64 Oxidation and Reduction MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Oxidation involves loss of electrons, increase in oxidation number or addition of oxygen, while reduction involves electron gain, decrease in oxidation number or removal of oxygen. The topic covers oxidising and reducing agents, oxidation-number changes, redox equations and the distinction between oxidation at the anode and reduction at the cathode.
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- A. loss of electrons and an increase in oxidation number
- B. gain of electrons and a decrease in oxidation number
- C. gain of hydrogen only
- D. loss of oxygen only
Explanation: The modern definition is in terms of electrons, so oxidation is loss and reduction is gain, remembered as OIL RIG.
Correct answer: loss of electrons and an increase in oxidation number- A. plus 2
- B. plus 6
- C. minus 2
- D. plus 4
Explanation: Hydrogen contributes plus 1 each and oxygen minus 2 each, so 2 plus x minus 8 equals zero and x is plus 6.
Correct answer: plus 6- A. loses electrons and is itself oxidised
- B. gains electrons and is itself reduced
- C. neither gains nor loses electrons
- D. always contains oxygen
Explanation: An oxidising agent oxidises something else by taking its electrons, so it is itself reduced in the process, and the same reasoning in…
Correct answer: gains electrons and is itself reduced- A. minus 2
- B. zero
- C. minus 1
- D. plus 2
Explanation: Hydrogen is plus 1, so the two oxygens must total minus 2 between them, giving minus 1 each, which is the exception to the usual rule of…
Correct answer: minus 1- A. plus 3
- B. plus 12
- C. plus 6
- D. plus 7
Explanation: Seven oxygens contribute minus 14, and the overall charge is minus 2, so the two chromium atoms must total plus 12, giving plus 6 each.
Correct answer: plus 6- A. a reducing agent because it gains electrons
- B. neither an oxidising nor a reducing agent
- C. a catalyst
- D. an oxidising agent because it accepts electrons from sodium
Explanation: Each chlorine atom accepts one electron and falls from zero to minus 1, so chlorine is reduced and is therefore the oxidising agent, while…
Correct answer: an oxidising agent because it accepts electrons from sodium- A. plus 1
- B. equal to its group number
- C. minus 1
- D. zero
Explanation: An uncombined element has not gained or lost any electrons, so its oxidation number is zero, and this holds for atoms such as helium and…
Correct answer: zero- A. X2YZ
- B. XY2Z2
- C. XYZ2
- D. XY2Z
Explanation: A neutral compound must have oxidation numbers summing to zero, and XY2Z2 gives plus 6, then two at minus 2 and two at minus 1, that is 6…
Correct answer: XY2Z2- A. Transfer of proton
- B. Transfer of electron
- C. Absorption of light
- D. Exchange of ions
Explanation: Oxidation is loss of electrons and reduction is gain, so a redox reaction is defined by electron transfer and by the change in oxidation…
Correct answer: Transfer of electron- A. Oxidation
- B. Reduction
- C. Redox
- D. Substitution
Explanation: Reduction takes place at the cathode, meaning the species gains electrons there.
Correct answer: Reduction- A. Reduction
- B. Oxidation
- C. Isomerization
- D. Crackling
Explanation: In the Bosch process, carbon monoxide combines with steam to form carbon dioxide and hydrogen: CO + H2O → CO2 + H2.
Correct answer: Oxidation- A. an anion
- B. a cation
- C. an anion - cation
- D. none of these
Explanation: Loss of an electron leaves a species with more protons than electrons, giving it a net positive charge.
Correct answer: a cation- A. N2O
- B. NO2
- C. HNO2
- D. HNO3
Explanation: In HNO3, hydrogen is +1 and oxygen contributes 3 x -2 = -6, so nitrogen must be +5: +1 + N - 6 = 0, giving N = +5.
Correct answer: HNO3- A. Number of electrons gained
- B. Number of electrons lost
- C. Apparent charge in compound
- D. Its vacancies
Explanation: Oxidation state is the apparent charge assigned to an atom when bonding electrons are treated as belonging to the more electronegative…
Correct answer: Apparent charge in compound- A. 7
- B. 6
- C. -7
- D. -6
Explanation: Let the oxidation number of each chromium atom be x: 2(+1) + 2x + 7(-2) = 0. Thus 2x - 12 = 0, so x = +6.
Correct answer: 6- A. valency
- B. coordination number
- C. oxidation number
- D. charge number
Explanation: Oxidation number is the apparent charge assigned to an atom by assuming that bonding electrons belong completely to the more…
Correct answer: oxidation number- A. oxidation
- B. reduction
- C. oxidation-reduction
- D. all of above represent same entity
Explanation: Reduction means a decrease in oxidation number because the species gains electrons or loses its formal positive character.
Correct answer: reduction- A. oxidation
- B. reduction
- C. redox
- D. decomposition
Explanation: Oxidation always occurs at the anode, whether the cell is galvanic or electrolytic; the electrode signs may change, but this reaction rule…
Correct answer: oxidation- A. Oxidation potential
- B. Reduction potential
- C. Redox potential
- D. emf of cell
Explanation: An oxidising agent accepts electrons, so a stronger oxidising agent has a greater tendency to undergo reduction.
Correct answer: Reduction potential- A. to form positive ions
- B. to form negative ions
- C. gain electrons
- D. all are possible
Explanation: A higher standard reduction potential means a greater tendency to gain electrons and be reduced.
Correct answer: to form positive ionsOxidation and Reduction MCQs: common questions
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