About Oxidation Reduction

Oxidation-reduction is the process by which a material's surface reduces its own oxidation state, thereby reducing the rate of oxidation. By controlling a material's oxidation state, it can be forced to reduce pollutants such as NOx and VOCs. Oxidation-reduction is a key strategy in many pollution control technologies. In metals and other elements that are naturally oxidizing (like iron), oxides form on their surfaces and can react with other nearby molecules to form compounds that are more stable. These oxides can be dissolved in water to remove them from the environment, or they can be converted into less reactive compounds through electrolysis or other chemical processes.

Many polymers also reduce their oxidation state through chemical reactions when exposed to air or light. Oxidation-reduction has been used for centuries to purify water by removing impurities. Since then, it has been used in a wide range of products, from medical equipment and electronics to construction materials and vehicles.

In some cases, it is used for the purpose of reducing emissions, such as in catalytic converters. The potential for oxidation-reduction is huge, but there are many challenges to overcome before it can reach its full potential. One of the biggest issues is cost because most materials are too expensive to produce in large quantities using traditional manufacturing methods. To solve this problem, new manufacturing techniques and cheaper alternatives will be necessary.

Following are some of the multiple choice questions on the Oxidation Reduction with answers that will help the students in developing their knowledge.

Oxidation Reduction MCQ

1. What is the oxidation state of sulphur in SO42- (aq)?

  • 4
  • 6
  • 2
  • 0

2. Which of the following elements is the strongest oxidizing agent?

  • Chlorine
  • Aluminium
  • Hydrogen
  • Lithium

3. What is the oxidation number assigned to manganese in KMnO4?

  • 7
  • 5
  • 4
  • 0

4. In the reaction 2Ca(s) + O2(g) --> 2CaO(s), calcium is __________

  • Reduced
  • Synthesized
  • Oxidized
  • None of the above

5. In which substance does sulfur have a negative oxidation number?

  • Na2S
  • SO2
  • S
  • Both A & B

6. What is the oxidation state of Nitrogen in N2 (g)?

  • 4
  • 6
  • 2
  • 0

7. Determine the oxidation number of chromium in CrO42-.

  • 5
  • 6
  • 4
  • 2

8. In a reaction, copper is reduced; its number of electrons has:

  • Increased
  • Decreased
  • Remained Constant
  • Varies Randomly

9. Which of these reagents can be used to convert Fe2+ to Fe3+ ion?I. Magnesium powderII. Potassium iodide solutionIII. Potassium hexacyanoferrate(II) solutionIV. Acidified potassium manganate(VII) solution

  • I and II only
  • II and III only
  • I, II and III only
  • I, II, III and IV

10. Which of the following statements is not true when zinc powder is added to dilute hydrochloric acid?

  • Zinc is oxidised
  • Chloride ion acts as an oxidising agent
  • Hydrogen ion is reduced
  • Electrons are transferred in the reaction

11. Which of the following reagents are able to change bromide ion in sodium bromide solution to bromine?I Sodium thiosulphate solutionII Acidified potassium dichromate(IV) solutionIII Acidified sodium chlorate(I) solutionIV Iodine solution

  • II and III only
  • I and IV only
  • I, II and IV only
  • I, II and III only

12. In the reaction Zn + H2O --> ZnO2 + H2 which element, if any, is oxidized?

  • Zinc
  • Hydrogen
  • Oxygen
  • None

13. A galvanic cell was created with a Calcium and a Copper cell. Which is the correct half equation at the anode?

  • Ca2+(aq)+2e−⟺ Ca(s)Ca^{2+}\left(aq\right)+2e^-\Longleftrightarrow\ Ca\left(s\right)Ca2+(aq)+2e−⟺ Ca(s)
  • Ca++e−⟺ Ca(s)Ca^++e^-\Longleftrightarrow\ Ca\left(s\right)Ca++e−⟺ Ca(s)
  • Cu2+(aq) + e− ⟺ Cu+(aq)Cu^{2+}\left(aq\right)\ +\ e^-\ \Longleftrightarrow\ Cu^+\left(aq\right)Cu2+(aq) + e− ⟺ Cu+(aq)
  • Cu2+(aq) + 2e− ⟺ Cu(s)Cu^{2+}\left(aq\right)\ +\ 2e^-\ \Longleftrightarrow\ Cu\left(s\right)Cu2+(aq) + 2e− ⟺ Cu(s)

14. Based on this equation: 2 I- + 2 Fe → 2Fe2+ + I2. Which of the following is true about the ionic equation?

  • Fe3+ is oxidized
  • Fe3+ is a reducing agent
  • I- is an oxidizing agent
  • I- donates electrons to Fe3+

15. Find the oxidation number of Ca in CaH2

  • -4
  • +2
  • +4
  • 0

16. Find the oxidation number of S in S2O4 2-

  • +3
  • +6
  • -6
  • -3

17. In an electrochemical cell, tin becomes a negative terminal when it is connected to

  • aluminium
  • lead
  • magnesium
  • zinc

18. A mixture of magnesium oxide, copper(II) oxide and zinc powder is heated in a crucible until no further changes are observed. After heating, the mixture contains:

  • magnesium, copper(II) oxide and zinc
  • magnesium oxide, copper and zinc oxide
  • magnesium oxide, copper(II) oxide and zinc
  • magnesium, copper and zinc oxide

19. What substance is oxidized in the following reaction?4Fe + 3O2 --> 2Fe2O3

  • Iron
  • Fluorine
  • Oxygen
  • None of these

20. In a redox reaction, spectator ions...

  • become oxidised
  • become reduced
  • remain unchanged
  • All of above

21. If an atom loses electrons during a chemical reaction, the atom was:

  • Oxidized
  • Reduced
  • Neutralized
  • Precipitated

22. Which of the following half reactions correctly represents a reduction half reaction?

  • Fe →Fe2+ + 2e-
  • Pb4+ + 2e- →Pb2+
  • 2O-2 →O2 + 4e-
  • Fe + 3e- →Fe3+

23. Gaining oxygen is an example of...

  • oxidation
  • reduction

24. Gaining hydrogen is an example of...

  • oxidation
  • reduction

25. Oxidation is the _________ of electrons.

  • loss
  • gain
  • sharing
  • transfer

26. Another name for a "oxidation-reduction" reaction is

  • chemical reaction
  • neutralization reaction
  • redox reaction
  • nuclear reaction

27. Substance that oxidizes another substance by accepting its electrons.

  • oxidising agent
  • reducing agent
  • combustion
  • None of these

28. A decrease in oxidation number.

  • Oxidation
  • combination
  • reduction
  • All of above

29. Which of the following is the balanced half -reaction for the oxidation of Cu to Cu+2?

  • Cu --> Cu+2
  • Cu + 2 e- --> Cu+2
  • Cu - 2e- --> Cu+2
  • Cu --> Cu+2 + 2 e-

30. The oxidation number of Hydrogen in KH potassium hydride equals:

  • -1
  • +1
  • 0
  • 2

31. An aqueous solution of potassium iodide turns from colourless to brown. What happens to the iodide ions?

  • Iodide ions are oxidised due to gain of electrons.
  • Iodide ions are oxidised due to loss of electrons.
  • Iodide ions are reduced due to loss of electrons.
  • Iodide ions are reduced due to gain of electrons.

32. What is the colour change of acidified KMnO4 solution when it is used as an oxidising agent?

  • from colourless to brown
  • from purple to colourless
  • from brown to colourless
  • from colourless to purple

33. What is the oxidation number of iodine in KIO3?

  • 5
  • 1
  • 0
  • -1

34. Reduction is the ___________ of electrons.

  • loss
  • gain
  • transfer
  • share

35. Which element was oxidized in the reaction below?Na + PbCl2 → Pb + NaCl

  • Na
  • Pb
  • Cl
  • No element was reduced

36. Which element was reduced in the reaction below?Na + PbCl2 → Pb + NaCl

  • Na
  • Pb
  • Cl
  • No element was reduced

37. An element's oxidation numbers became more negative during a reaction. What happened to that element?

  • It was oxidized
  • It was reduced
  • It was both oxidized and reduced
  • It was neither oxidized nor reduced

38. An element's oxidation numbers changed from zero to +2 during a reaction. What happened to that element?

  • It was oxidized
  • It was reduced
  • It was both oxidized and reduced
  • It was neither oxidized nor reduced

39. An element's oxidation numbers remain the same during a reaction. What happened to that element?

  • It was oxidized
  • It was reduced
  • It was both oxidized and reduced
  • It was neither oxidized nor reduced

40. What is the oxidation number on the nitrogen in NO2-?

  • -1
  • +3
  • -3
  • +4

41. What is the oxidation number on the nitrogen in Mg3N2?

  • 0
  • -2
  • -3
  • +3

42. What is the oxidation number on the nitrogen in NO?

  • 0
  • -1
  • -2
  • +2

43. If an atom lost electrons, it...

  • was burned
  • was reduced
  • was oxidized
  • it became negative

44. Of the 5 types of reactions, which one(s) are oxidation-reduction?

  • all of them
  • only double replacement
  • double replacement and combustion
  • all of them except double replacement

45. Which of the following is NOT an example of an oxidation reduction reaction?

  • metal rusting
  • acid neutralizing base
  • burning methane
  • photosynthesis

46. Which of the following has an oxidation number of zero on the chlorine atom?

  • NaCl
  • Cl2
  • Cl-
  • ClO3-

47. If oxidation happened, then...

  • something gained electrons
  • reduction also happened
  • flames are always involved
  • oxygen is always involved

48. During the process of reduction, _________________

  • protons are lost.
  • protons are gained.
  • electrons are lost.
  • electrons are gained
  • neutrons are lost.

49. Which statement is true:Mg → Mg2+ + 2e–

  • Mg gains 2 electrons
  • Mg2+ loses 2 electrons
  • Mg loses 1 electron
  • Mg loses 2 electrons

50. In a redox reaction, the species reduced

  • gains electrons and is the oxidizing agent
  • loses electrons and is the oxidizing agent
  • loses electrons and is the reducing agent
  • gains electrons and is the reducing agent

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