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1. A reaction involving the simultaneous loss and gain of electrons between reactants is called a:
A. Redox reaction
B. Neutralisation reaction
C. Precipitation reaction
D. Decomposition reaction only
Answer: A. Redox reaction
Explanation: Redox (reduction-oxidation) reactions involve the transfer of electrons, with one species losing electrons while another gains them.
2. The process involving the loss of electrons by a substance is called:
A. Oxidation
B. Reduction
C. Neutralisation
D. Hydrolysis
Answer: A. Oxidation
Explanation: Oxidation is specifically defined as the process in which a substance loses one or more electrons.
3. The process involving the gain of electrons by a substance is called:
A. Reduction
B. Oxidation
C. Ionisation
D. Precipitation
Answer: A. Reduction
Explanation: Reduction is the process in which a substance gains one or more electrons, decreasing its oxidation state.
4. The substance that gets oxidised in a redox reaction, thereby causing reduction of another substance, is called the:
A. Reducing agent
B. Oxidising agent
C. Catalyst
D. Product
Answer: A. Reducing agent
Explanation: A reducing agent donates electrons to another species, causing that species to be reduced, while it itself becomes oxidised.
5. The substance that gets reduced in a redox reaction, thereby causing oxidation of another substance, is called the:
A. Oxidising agent
B. Reducing agent
C. Catalyst
D. Inhibitor
Answer: A. Oxidising agent
Explanation: An oxidising agent accepts electrons from another species, causing that species to be oxidised, while it itself becomes reduced.
6. The oxidation number of an atom in its elemental (uncombined) state is always:
A. Zero
B. One
C. Negative
D. Equal to its atomic number
Answer: A. Zero
Explanation: By convention, any element in its free, uncombined form has an oxidation number of exactly zero.
7. The oxidation number of hydrogen in most compounds is generally:
A. +1
B. -1
C. 0
D. +2
Answer: A. +1
Explanation: In most compounds, hydrogen typically exhibits an oxidation number of +1, except in metal hydrides where it is -1.
8. The oxidation number of oxygen in most compounds (excluding peroxides) is generally:
A. -2
B. +2
C. 0
D. -1
Answer: A. -2
Explanation: Oxygen commonly has an oxidation number of -2 in most compounds, with exceptions like peroxides where it is -1.
9. The sum of oxidation numbers of all atoms in a neutral compound is always:
A. Zero
B. One
C. Equal to the atomic number
D. Negative
Answer: A. Zero
Explanation: For any electrically neutral compound, the sum of the oxidation numbers of all constituent atoms must total zero.
10. The sum of oxidation numbers of all atoms in a polyatomic ion equals:
A. The net charge on the ion
B. Always zero
C. The atomic number of the central atom
D. The total number of atoms
Answer: A. The net charge on the ion
Explanation: For a polyatomic ion, the sum of individual atomic oxidation numbers must equal the overall charge carried by that ion.
11. A reaction in which the same element is simultaneously oxidised and reduced is called a:
A. Disproportionation reaction
B. Combination reaction only
C. Displacement reaction only
D. Neutralisation reaction
Answer: A. Disproportionation reaction
Explanation: Disproportionation reactions involve a single element undergoing both oxidation and reduction simultaneously within the same reaction.
12. The method of balancing redox reactions based on changes in oxidation number is called the:
A. Oxidation number method
B. Ion-electron method only
C. Titration method
D. Gravimetric method
Answer: A. Oxidation number method
Explanation: The oxidation number method balances redox equations by equating the total increase and decrease in oxidation numbers of the species involved.
13. The method of balancing redox reactions by splitting them into separate oxidation and reduction half-reactions is called the:
A. Ion-electron (half-reaction) method
B. Oxidation number method only
C. Direct balancing method
D. Combustion method
Answer: A. Ion-electron (half-reaction) method
Explanation: The ion-electron method involves writing and balancing separate half-reactions for oxidation and reduction before combining them.
14. A cell that converts chemical energy into electrical energy through spontaneous redox reactions is called a:
A. Galvanic (voltaic) cell
B. Electrolytic cell
C. Fuel tank
D. Battery casing only
Answer: A. Galvanic (voltaic) cell
Explanation: A galvanic or voltaic cell harnesses spontaneous redox reactions to generate a flow of electric current, converting chemical to electrical energy.
15. A cell that uses electrical energy to drive a non-spontaneous redox reaction is called a/an:
A. Electrolytic cell
B. Galvanic cell
C. Fuel cell only
D. Concentration cell only
Answer: A. Electrolytic cell
Explanation: An electrolytic cell requires an external electrical energy source to force a non-spontaneous redox reaction to proceed.
16. In an electrochemical cell, the electrode at which oxidation occurs is called the:
A. Anode
B. Cathode
C. Salt bridge
D. Electrolyte
Answer: A. Anode
Explanation: By convention, the anode is defined as the electrode where oxidation takes place, regardless of the type of cell.
17. In an electrochemical cell, the electrode at which reduction occurs is called the:
A. Cathode
B. Anode
C. Salt bridge only
D. Electrolyte only
Answer: A. Cathode
Explanation: The cathode is defined as the electrode where reduction reactions occur within an electrochemical cell.
18. The component of a galvanic cell that maintains electrical neutrality by allowing ion flow between half-cells is called the:
A. Salt bridge
B. Anode
C. Cathode
D. External circuit
Answer: A. Salt bridge
Explanation: The salt bridge allows the movement of ions between the two half-cells, maintaining charge balance as the reaction proceeds.
19. The standard electrode potential of the standard hydrogen electrode (SHE) is defined as:
A. 0.00 V
B. 1.00 V
C. -1.00 V
D. 2.00 V
Answer: A. 0.00 V
Explanation: By convention, the standard hydrogen electrode is assigned a reference potential of exactly 0.00 volts.
20. A species with a higher tendency to get reduced (gain electrons) is considered a:
A. Stronger oxidising agent
B. Stronger reducing agent
C. Neutral species
D. Catalyst
Answer: A. Stronger oxidising agent
Explanation: Since oxidising agents themselves get reduced by accepting electrons, a greater tendency for reduction indicates a stronger oxidising agent.
21. The oxidation state of manganese in KMnO₄ is:
A. +7
B. +2
C. +4
D. 0
Answer: A. +7
Explanation: In KMnO₄, since K is +1 and each O is -2, balancing the overall neutral charge gives manganese an oxidation state of +7.
22. The oxidation state of chromium in K₂Cr₂O₇ is:
A. +6
B. +3
C. +2
D. 0
Answer: A. +6
Explanation: In K₂Cr₂O₇, with K at +1 and O at -2, balancing the compound's overall neutral charge gives each chromium atom an oxidation state of +6.
23. The rusting of iron is an example of a:
A. Redox reaction involving oxidation by atmospheric oxygen
B. Neutralisation reaction
C. Precipitation reaction
D. Non-redox physical change
Answer: A. Redox reaction involving oxidation by atmospheric oxygen
Explanation: Rusting involves the oxidation of iron metal by atmospheric oxygen, making it a classic example of a naturally occurring redox process.
24. Reactions between metals and acids, releasing hydrogen gas, are typically classified as:
A. Redox reactions
B. Non-redox acid-base reactions
C. Precipitation reactions
D. Complexation reactions
Answer: A. Redox reactions
Explanation: These reactions involve the metal being oxidised while hydrogen ions from the acid are reduced to hydrogen gas, making them redox reactions.
25. Corrosion of metals is generally an example of a slow, naturally occurring:
A. Oxidation process
B. Reduction process only
C. Neutralisation process
D. Precipitation process
Answer: A. Oxidation process
Explanation: Corrosion typically involves the gradual oxidation of a metal's surface when exposed to environmental agents like oxygen and moisture.
26. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, zinc is:
A. Oxidised, acting as the reducing agent
B. Reduced, acting as the oxidising agent
C. Unaffected by the reaction
D. Acting as a catalyst only
Answer: A. Oxidised, acting as the reducing agent
Explanation: Zinc loses electrons to form Zn²⁺, meaning it is oxidised and therefore acts as the reducing agent in this reaction.
27. In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, copper ions are:
A. Reduced, acting as the oxidising agent
B. Oxidised, acting as the reducing agent
C. Unaffected by the reaction
D. Acting as a catalyst
Answer: A. Reduced, acting as the oxidising agent
Explanation: Copper ions gain electrons to form solid copper, meaning they are reduced and therefore act as the oxidising agent.
28. A balanced redox equation must satisfy conservation of both mass and:
A. Charge
B. Volume
C. Temperature
D. Colour
Answer: A. Charge
Explanation: In addition to conserving the number of atoms (mass), a properly balanced redox equation must also ensure that total charge is conserved on both sides.
29. Electrolysis is a process that uses electrical energy to bring about a:
A. Non-spontaneous chemical reaction
B. Spontaneous chemical reaction only
C. Physical change only
D. Neutral reaction with no electron transfer
Answer: A. Non-spontaneous chemical reaction
Explanation: Electrolysis specifically involves supplying external electrical energy to force a chemical reaction that would not otherwise occur spontaneously.
30. The concept of oxidation number is useful primarily for:
A. Identifying and balancing redox reactions systematically
B. Measuring the physical size of atoms
C. Determining the boiling point of compounds
D. Calculating molar mass only
Answer: A. Identifying and balancing redox reactions systematically
Explanation: Oxidation numbers provide a systematic way to track electron transfer, making it easier to identify and balance redox reactions.
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