Redox Reactions – Multiple Choice Questions

Q1. For the redox reactionMnO₄^– + C₂O₄^2- + H⁺ → Mn²⁺ + CO₂ + H₂O .The correct coefficients of the reactants for the balanced reaction are:

1. MnO₄^– = 2           C₂O₄^2- = 5                H⁺ = 16 
2. MnO₄^–  = 16       C₂O₄^2- = 5                H⁺ = 2
3. MnO₄^–  = 5    C₂O₄^2- = 16             H⁺ = 2
4. MnO₄^–  = 2    C₂O₄^2- = 16               H⁺ = 5  

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Q2. A substance (atom, ion or molecule) which can readily accept electrons from other substances is called

1. Oxidising agent
2. Reducing agent
3. None of them
4. both a and b

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Q3. The oxidation number of Mg in Mg⁺² is

1. +2
2. +1
3. -2
4. -1

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Q4. 2 K₄ [Fe (CN)₆]_(aq) + H₂O_2 (aq) → 2 K₃ [Fe (CN)₆]_(aq) + 2KOH_(aq) is an example of

1. Oxidation
2. Reduction
3. Replacement
4. Addition

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Q5. The balanced half reaction is:

1. MnO₄^-1(aq) + 2H₂O(l) + 3e^– → MnO₂(s) + 4OH^–(aq)
2. MnO₄^-1(aq) + 2H₂O(l)  → MnO₂(s) + 4OH^–(aq)
3. MnO₄^-1(aq) + 2H₂O(l) + 3e^– → MnO₂(s) + OH^–(aq)
4. 4MnO₄^-1(aq) + 2H₂O(l) → MnO₂(s) + 4OH^–(aq)

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Q6. The process in which the strength of an unknown solution is calculated using a known standard solution is known as

1. titration
2. oxidation
3. reduction
4. none of these

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Q7. In Ni(CO)₄ the oxidation number of Ni is

1. 4
2. 2
3. 8
4. 0

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Q8. In 2Na_(S) + Cl₂ → 2 NaCl _(S) ; The oxidising agent is

1. Sodium
2. Chlorine
3. Sodium chloride
4. None of these

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Q9. Given the standard reduction potentials:Zn²⁺/Zn = – 0.74 V, Cl₂/Cl^– = 1.36 V, H⁺/1/2H₂ = 0 V and Fe³⁺/Fe²⁺ = 0.77 V. The order of increasing strength as reducing agent is

1. Zn, H₂, Fe²⁺, Cl^–
2. H₂, Zn, Fe²⁺, Cl^–
3. Cl^–, Fe²⁺,Zn, H₂
4. Cl^–, Fe²⁺, H_2, Zn

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Q10. Find out EMF of cell, Zn|Zn²⁺_(1M) || Cu²⁺_(1M)|CuE^o for Zn²⁺/Zn = -0.76 V, E^o for Cu²⁺/Cu = +0.34 V

1. +1.10 V
2. -1.10 V
3. -0.76 V
4. -0.42 V

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Q11. Which of the following is NOT true about the oxidation state of oxygen?

1. It shows oxidation state +3.
2. It shows oxidation state +2.
3. It shows oxidation state -1/2.
4. It shows oxidation states -1.

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Q12. When Zinc rod is dipped in copper nitrate solution, the blue colour of copper nitrate solution starts fading. The substance that undergoes oxidation is

1. Zn_(s)
2. Zn²⁺
3. Cu_(s)
4. Cu²⁺

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Q13. The standard electrode potentials, K⁺/K= -2.93V, Ag⁺/Ag = 0.80V, the electrode which is negatively charged is

1. Ag⁺/Ag
2. K⁺/K
3. Any of the two
4. None of them

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Q14. The oxidation and reduction half reactions of the reaction2Al_(s) + 3Cu²⁺_(aq) → 2Al³⁺_(aq) + 3Cu_(s) are

1. Oxidation: 2Al_(s)  →   Al³⁺_(aq) + 3e^– ] x 2    Reduction: Cu²⁺ + 2e^– → Cu_(s) ] x 3          
2. Oxidation: Al_(s)   →  Al³⁺ + 3e^– ] x 2           Reduction: Cu²⁺ + 2e^– → Cu_(s) ] x 3          
3. Oxidation: Al_(s) → Al³⁺_(aq) + 3e^– ] x 2            Reduction: 2Cu²⁺_(aq) + 2e^–  →  Cu_(s) ] x 3      
4. Oxidation: Al_(s)  →    Al³⁺_(aq) + 3e^– ] x 2         Reduction: Cu²⁺_(aq) + 2e^– →  Cu_(s) ] x 2        

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Q15. To balance the oxygen atom in the given reaction in acidic medium,Cr₂O₇^2-_(aq) → Cr³⁺_(aq) we will,

1. Add O on left side
2. Add water (H₂O) on left side
3. Add water (H₂O) on right side
4. Add O on right side

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Q16. In which of the following method, two half equations are balanced separately and then added together to give balanced equation?

1. Half reaction method
2. Reducing agent method
3. Oxidizing agent method
4. Reluctant method

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Q17. A substance (atom, ion or molecule) which can readily loose electrons to other substances is called

1. Oxidising agent
2. Reducing agent
3. None of them
4. both a and b

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Q18. To balance the charge in the oxidation half reaction Fe²⁺_(aq) → Fe³⁺_(aq)

1. Add an electron on reactant side
2. Add an electron on product side
3. Add two electrons on reactant side
4. Add two electrons on product side

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Q19. A standard hydrogen electrode has zero electrode potential because

1. Hydrogen is easiest to oxidize.
2. The electrode potential is assumed to be zero.
3. Hydrogen atom has only one electron.
4. Hydrogen is the lightest element.

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Q20. Balanced ionic equation for the reaction of Potassium Dichromate (VI) K₂Cr₂O₇ with Sodium Sulphite Na₂SO₃ in acid solution to give Chromium (III) ion and sulphate ion is

1. Cr₂O₇^-2_(aq) + 3SO₃^2-_(aq) + 8H⁺_(aq) → 2Cr³⁺_(aq) + 3SO₄^2-_(aq) + 4H₂O_(liq)
2. Cr₂O₇^-2_(aq) + 2SO₃^2-_(aq) + 8H⁺_(aq) → 2Cr³⁺_(aq) + 3SO₄^2-_(aq) + 4H₂O_(liq)
3. Cr₂O₇^-2_(aq) + 3SO₃^2-_(aq) + 5H⁺_(aq) → 2Cr³⁺_(aq) + 3SO₄^2-_(aq) + 4H₂O_(liq)
4. Cr₂O₇^-2_(aq) + 3SO₃^2-_(aq) + 8H⁺_(aq) → 2Cr³⁺_(aq) + 5SO₄^2-_(aq) + 4H₂O_(liq)

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Q21. In the following reaction3Br₂ + 6CO₃^2- + 3H₂O →  5Br ^– + BrO₃^– + 6HCO₃^–

1. Bromine is oxidized, carbonate is reduced
2. Bromine is reduced, carbonate is oxidized
3. Bromine is neither reduced nor oxidized
4. Bromine is reduced as well as oxidized

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Q22. The oxidation number of Fe in K₄Fe(CN)₆ is

1. +6
2. +4
3. +3
4. +2

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Q23. Nitrous Acid acts as a:

1. Reducing agent
2. Oxidising agent
3. Oxidising as well as reducing agent
4. None of the above

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Q24. Those reactions in which oxidation and reduction takes place simultaneously are known as

1. Redox reaction
2. Addition reaction
3. Chemical reaction
4. None of the above

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Q25. In the reaction H₂S_(g) + Cl_2(g) → 2HCl_(g) + S_(s), H₂S is

1. Oxidised
2. Reduced
3. None of them
4. both a and b

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Q26. The oxidation number of Ca in Ca⁺² is

1. +2
2. -2
3. +1
4. -1

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Q27. For the reaction Fe²⁺_(aq) + Cr₂O₇^2-_(aq) → Fe³⁺_(aq) + Cr³⁺_(aq) , the reduction half reaction is,

1. Cr₂O₇^2- _(aq) → Cr³⁺ _(aq)
2. Fe²⁺ _(aq) → Fe³⁺ _(aq)
3. Fe²⁺ _(aq) + Cr₂O₇^2- _(aq) → Fe³⁺ _(aq) + Cr³⁺ _(aq)
4. None of these

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Q28. Which one of the following is reducing agent?

1. Ozone
2. Chlorine
3. FeCl₃
4. Na₂S₂O₃

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Q29. By what unit the oxidation number changes for underline elements in the following reaction-Zn + HNO₃ → NH₄NO₃ + Zn (NO₃)₂ + H₂O

1. 4 units
2. 2 units
3. 6 units
4. 8 units

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Q30. Pick the odd one out

1. Combination redox reaction
2. Displacement redox reaction
3. Catalysis redox reaction
4. Decomposition redox reaction

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Q31. According to classical idea of redox reactions the given example is of2 Mg_(s) + O_2 (g) → 2 MgO_(s)

1. Oxidation
2. Reduction
3. Redox reaction
4. All the above

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Q32. The conversion of K₂Cr₂O₇ into Cr₂ (SO₄)₃ is a process of

1. Oxidation
2. Reduction
3. Decomposition
4. Substitution

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Q33. How many electrons are transferred during following change?2I^–_(aq) → I_2(s)

1. 4 electrons
2. 0 electrons
3. 2 electrons
4. 1 electron

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Q34. In an electrochemical cell represented as,Zn | Zn²⁺₍c₁₎ || Cu²⁺₍c₂₎ | Cuso in this cell,

1. Zn is oxidized
2. Zn is reduced
3. Cu is oxidized
4. Cu is reduced

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Q35. The oxidation number of an element in its free state is always

1. -1
2. 1
3. 0
4. None of these

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Q36. The oxidation half reaction for following reaction isFe²⁺(aq) + Cr₂O₇^2-(aq) → Fe³⁺ (aq) + Cr³⁺(aq)

1. Fe²⁺ (aq) → Fe³⁺(aq)
2. Cr₂O₇^2-(aq) → Cr³⁺(aq)
3. Fe³⁺(aq) → Fe²⁺ (aq)
4. Cr³⁺(aq) → Cr₂O₇^2-(aq)

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Q37. The reaction H₂S + H₂O₂ → SO₂ + 2H₂O manifests

1. Oxidizing action of H₂O₂
2. Reducing nature of H₂O₂
3. Acidic nature of H₂O₂
4. Alkaline nature of H₂O₂

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Q38. A cell is prepared by dipping a chromium rod in 1M Cr₂(SO₄)₃ solution and an iron rod in 1M FeSO₄ solution. The standard reduction potentials of Chromium and Iron electrodes are -0.75 V and -0.45 V respectively. What will be the standard EMF of the cell?

1. – 0.30 V
2. +0.30 V
3. +0.47 V
4. -0.47 V

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Q39. We can balance the following ionic equation by adding 6Fe²⁺(aq) + Cr₂O₇^2-(aq)  → 6 Fe³⁺(aq) +2Cr ³⁺(aq)

1. 7 H₂O on RHS and 14 H⁺ on LHS
2.  7 H₂O on LHS and 14 H⁺ on RHS
3. 3H₂O on RHS and 6 H⁺ on LHS
4. 3H₂O on LHS and 6 H⁺ on RHS

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Q40. Which of the following is disproportionation reaction?

1.   4 KClO₃ → 3KClO₄ + KCl
2. C(s) + O₂ (g) → CO₂(g)
3. CaCO₃ (s) → CaO(s) + CO₂(g)
4. CuSO₄(aq) + Zn (s) → Cu(s) + ZnSO₄ (aq)

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