Oxidation and reduction concepts, oxidation numbers, balancing redox reactions - Question Bank

1. In the reaction $C + O_2 → CO_2$, Carbon is oxidized from an oxidation state of 0 to:
A) +2
B) +4
C) -2
D) -4
2. Which statement is correct regarding redox reactions?
A) Oxidation and reduction occur independently.
B) Oxidation can occur without reduction.
C) Reduction can occur without oxidation.
D) Oxidation and reduction occur simultaneously.
3. The oxidation number of an element in an ion is equal to:
A) Zero
B) The charge of the ion
C) The number of atoms in the ion
D) The number of electrons lost
4. In balancing a redox reaction by the ion-electron method, electrons are added to balance:
A) Mass
B) Charge
C) Number of atoms
D) The overall reaction
5. The half-reaction representing reduction is:
A) Loss of electrons
B) Gain of electrons
C) Loss of neutrons
D) Gain of neutrons
6. The half-reaction representing oxidation is:
A) Gain of electrons
B) Loss of electrons
C) Gain of protons
D) Loss of protons
7. Which element is reduced in the reaction $2KMnO_4 + 16HCl → 2KCl + 2MnCl_2 + 5Cl_2 + 8H_2O$?
A) Potassium (K)
B) Manganese (Mn)
C) Chlorine (Cl)
D) Hydrogen (H)
8. Which element is oxidized in the reaction $2KMnO_4 + 16HCl → 2KCl + 2MnCl_2 + 5Cl_2 + 8H_2O$?
A) Potassium (K)
B) Manganese (Mn)
C) Chlorine (Cl)
D) Oxygen (O)
9. In the reaction $SO_2 + 2H_2S → 3S + 2H_2O$, Hydrogen sulfide ($H_2S$) acts as:
A) An oxidizing agent
B) A reducing agent
C) Both oxidizing and reducing agent
D) Neither
10. In the reaction $SO_2 + 2H_2S → 3S + 2H_2O$, Sulfur dioxide ($SO_2$) acts as:
A) An oxidizing agent
B) A reducing agent
C) Both oxidizing and reducing agent
D) Neither
11. Which of the following reactions is NOT a redox reaction?
A) $H_2 + Cl_2 → 2HCl$
B) $2KClO_3 → 2KCl + 3O_2$
C) $HCl + NaOH → NaCl + H_2O$
D) $Zn + CuSO_4 → ZnSO_4 + Cu$
12. What is the oxidation number of Phosphorus in $P_4O_{10}$?
A) +5
B) +4
C) -5
D) -4
13. What is the oxidation number of Nitrogen in $NO_2$?
A) +2
B) +4
C) -2
D) -4
14. What is the oxidation number of Nitrogen in $NH_3$?
A) +3
B) -3
C) +1
D) -1
15. What is the oxidation number of Manganese in $KMnO_4$?
A) +7
B) +6
C) +4
D) +2
16. What is the oxidation number of Chromium in $K_2Cr_2O_7$?
A) +6
B) +7
C) +3
D) +2
17. What is the oxidation number of Carbon in $CH_4$?
A) +4
B) +2
C) -2
D) -4
18. What is the oxidation number of Carbon in $CO_2$?
A) +2
B) +4
C) -2
D) -4
19. In the reaction $I_2 + S_2O_3^{2-} → 2I^- + S_4O_6^{2-}$, Thiosulfate ion ($S_2O_3^{2-}$) is:
A) Oxidized
B) Reduced
C) Neither oxidized nor reduced
D) Both oxidized and reduced
20. In the reaction $I_2 + S_2O_3^{2-} → 2I^- + S_4O_6^{2-}$, Iodine ($I_2$) is:
A) Oxidized
B) Reduced
C) Neither oxidized nor reduced
D) Both oxidized and reduced
21. The species that gets reduced in a redox reaction is the:
A) Oxidizing agent
B) Reducing agent
C) Both oxidizing and reducing agent
D) Catalyst
22. The species that gets oxidized in a redox reaction is the:
A) Oxidizing agent
B) Reducing agent
C) Both oxidizing and reducing agent
D) Spectator ion
23. In the reaction $MnO_4^- + 5Fe^{2+} + 8H^+ → Mn^{2+} + 5Fe^{3+} + 4H_2O$, the oxidation number of Iron changes from:
A) +3 to +2
B) +2 to +3
C) 0 to +2
D) +2 to 0
24. In the reaction $MnO_4^- + 5Fe^{2+} + 8H^+ → Mn^{2+} + 5Fe^{3+} + 4H_2O$, the oxidation number of Manganese changes from:
A) +2 to +7
B) +7 to +2
C) +4 to +2
D) +7 to +4
25. Which of the following is an example of disproportionation reaction?
A) $Cl_2 + 2KI → 2KCl + I_2$
B) $2Na + Cl_2 → 2NaCl$
C) $2H_2O_2 → 2H_2O + O_2$
D) $Zn + 2HCl → ZnCl_2 + H_2$
26. Which of the following is an example of intramolecular redox reaction?
A) $Zn + CuSO_4 → ZnSO_4 + Cu$
B) $2H_2 + O_2 → 2H_2O$
C) $KClO_3 → KCl + O_2$
D) $HCl + NaOH → NaCl + H_2O$
27. Balancing redox reactions in basic medium typically involves adding $OH^-$ and $H_2O$ to balance oxygen and hydrogen atoms respectively, and then:
A) Adding $H^+$ to both sides
B) Adding electrons to balance charge
C) Multiplying by a stoichiometric coefficient
D) Ignoring the charge balance
28. In basic medium, to balance a redox reaction, which species is added to balance hydrogen atoms?
A) $H^+$
B) $OH^-$
C) $H_2O$
D) Electrons
29. In basic medium, to balance a redox reaction, which species is added to balance oxygen atoms?
A) $H^+$
B) $OH^-$
C) $H_2O$
D) Electrons
30. In acidic medium, to balance a redox reaction, which species is added to balance hydrogen atoms?
A) $H^+$
B) $OH^-$
C) $H_2O$
D) Electrons
31. In acidic medium, to balance a redox reaction, which species is added to balance oxygen atoms?
A) $H^+$
B) $OH^-$
C) $H_2O$
D) Electrons
32. To balance a redox reaction using the oxidation number method, the change in oxidation numbers on both sides must be:
A) Equal
B) Opposite
C) Zero
D) Doubled
33. In the reaction $Zn + CuSO_4 → ZnSO_4 + Cu$, Copper is:
A) Oxidized
B) Reduced
C) Neither oxidized nor reduced
D) A reducing agent
34. In the reaction $Zn + CuSO_4 → ZnSO_4 + Cu$, Zinc is:
A) Oxidized
B) Reduced
C) Neither oxidized nor reduced
D) An oxidizing agent
35. Which of the following is an oxidizing agent?
A) Sulfur Dioxide ($SO_2$)
B) Ammonia ($NH_3$)
C) Potassium Dichromate ($K_2Cr_2O_7$)
D) Sodium Chloride ($NaCl$)
36. Which of the following is a reducing agent?
A) Oxygen
B) Chlorine
C) Hydrogen Sulfide ($H_2S$)
D) Potassium Permanganate ($KMnO_4$)
37. The process of losing oxygen or gaining hydrogen is considered:
A) Oxidation
B) Reduction
C) Combustion
D) Synthesis
38. The process of gaining oxygen or losing hydrogen is considered:
A) Reduction
B) Oxidation
C) Acid-base reaction
D) Decomposition
39. In the compound $H_2O_2$ (hydrogen peroxide), what is the oxidation number of Oxygen?
A) -1
B) -2
C) +1
D) 0
40. In the polyatomic ion $SO_4^{2-}$, what is the oxidation number of Sulfur (S)?
A) +2
B) +4
C) +6
D) -2
41. What is the oxidation number of Fluorine in all its compounds?
A) 0
B) +1
C) -1
D) Variable
42. What is the oxidation number of Hydrogen when bonded to metals?
A) +1
B) -1
C) 0
D) Variable
43. What is the oxidation number of Hydrogen when bonded to non-metals?
A) +1
B) -1
C) 0
D) +2
44. What is the oxidation number of Oxygen in most of its compounds?
A) +2
B) -2
C) +1
D) 0
45. In the reaction $2Na + Cl_2 → 2NaCl$, what is the oxidation number of Chlorine (Cl)?
A) 0
B) +1
C) -1
D) -2
46. In the reaction $2Na + Cl_2 → 2NaCl$, what is the oxidation number of Sodium (Na)?
A) 0
B) +1
C) -1
D) +2
47. The sum of oxidation numbers of all atoms in a neutral molecule is:
A) Always positive
B) Always negative
C) Zero
D) Equal to the number of atoms
48. What is the oxidation number of an element in its free and uncombined state?
A) -1
B) 0
C) +1
D) Variable
49. In a chemical reaction, the gain of electrons is called:
A) Oxidation
B) Reduction
C) Combustion
D) Polymerization
50. Which process involves the loss of electrons?
A) Reduction
B) Oxidation
C) Neutralization
D) Dissociation
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