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1. Q1Easy

   Which of the following reactions is an example of a **displacement reaction** where a metal is displaced from its compound?

   • A.Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
   • B.2H₂O₂(l) → 2H₂O(l) + O₂(g)
   • C.2NO₂(g) + 2OH⁻(aq) → NO₂⁻(aq) + NO₃⁻(aq) + H₂O(l)
   • D.N₂(g) + O₂(g) → 2NO(g)
   Answer: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

   Explanation: In this reaction, zinc displaces copper from copper sulfate, forming zinc sulfate and metallic copper. This is a classic example of a metal displacement reaction.

2. Q2Easy

   Which of the following reactions is an example of a **combination redox reaction**?

   • A.N₂(g) + O₂(g) → 2NO(g)
   • B.2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g)
   • C.Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
   • D.3ClO⁻ → 2Cl⁻ + ClO₃⁻
   Answer: N₂(g) + O₂(g) → 2NO(g)

   Explanation: This reaction involves the combination of two elemental substances (N₂ and O₂) to form a single compound (NO), which is a combination redox reaction.

3. Q3Easy

   What is the **oxidation state** of cobalt in CoCl₂?

   • A.+1
   • B.+2
   • C.+3
   • D.+4
   Answer: +2

   Explanation: In CoCl₂, the oxidation state of cobalt can be calculated as follows: Let the oxidation state of Co be x. Then, x + 2*(-1) = 0 → x = +2.

4. Q4Easy

   What is the **role of H₂S gas** in testing for Cu²⁺ ions?

   • A.Formation of black CuS precipitate
   • B.Formation of blue CuSO₄ solution
   • C.Formation of white Cu(OH)₂ precipitate
   • D.Formation of green CuCO₃ precipitate
   Answer: Formation of black CuS precipitate

   Explanation: H₂S reacts with Cu²⁺ ions to form black CuS precipitate, which is a sensitive test for the presence of copper ions.

5. Q5Medium

   In the reaction between copper metal and silver nitrate solution, which species is **oxidized**?

   • A.Cu(s)
   • B.Ag⁺(aq)
   • C.NO₃⁻(aq)
   • D.H₂O(l)
   Answer: Cu(s)

   Explanation: Copper metal (Cu) loses electrons and is oxidized to Cu²⁺ ions, while Ag⁺ ions gain electrons and are reduced to silver metal (Ag).

6. Q6Medium

   What is the **oxidation state** of chlorine in ClO₃⁻?

   • A.+1
   • B.+3
   • C.+5
   • D.+7
   Answer: +5

   Explanation: The oxidation state of chlorine in ClO₃⁻ can be calculated as follows: Let the oxidation state of Cl be x. Then, x + 3*(-2) = -1 → x = +5.

7. Q7Medium

   In a Daniell cell, which electrode undergoes **oxidation**?

   • A.Zinc electrode (anode)
   • B.Copper electrode (cathode)
   • C.Salt bridge
   • D.Electrolyte solution
   Answer: Zinc electrode (anode)

   Explanation: In a Daniell cell, zinc is oxidized to Zn²⁺ ions at the anode, losing electrons to the external circuit, while Cu²⁺ ions are reduced to Cu at the cathode.

8. Q8Medium

   What is the role of the **salt bridge** in a Daniell cell?

   • A.To complete the circuit by allowing ion migration
   • B.To act as an electrode
   • C.To store electrical energy
   • D.To increase the voltage
   Answer: To complete the circuit by allowing ion migration

   Explanation: The salt bridge maintains electrical neutrality in the cell by allowing ions to move between the two half-cells, thus completing the circuit.

9. Q9Hard

   Which of the following is an example of a **disproportionation reaction**?

   • A.3ClO⁻ → 2Cl⁻ + ClO₃⁻
   • B.Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
   • C.2PbO₂(s) → 2PbO(s) + O₂(g)
   • D.N₂(g) + O₂(g) → 2NO(g)
   Answer: 3ClO⁻ → 2Cl⁻ + ClO₃⁻

   Explanation: In this reaction, the same species (ClO⁻) undergoes both oxidation and reduction, forming Cl⁻ (reduced) and ClO₃⁻ (oxidized).

10. Q10Hard

    Which of the following is the **oxidizing agent** in the reaction: Cu₂O(s) + Cu₂S(s) → 6Cu(s) + SO₂(g)?

    • A.Cu₂O
    • B.Cu₂S
    • C.SO₂
    • D.Cu
    Answer: Cu₂O

    Explanation: In this reaction, Cu₂O is reduced to Cu, and Cu₂S is oxidized to SO₂. Therefore, Cu₂O acts as the oxidizing agent.

11. Q11Hard

    What is the **oxidation state** of iron in Fe₃O₄?

    • A.+2
    • B.+3
    • C.+8/3
    • D.+4
    Answer: +8/3

    Explanation: In Fe₃O₄, the oxidation states of iron are not all the same. Two of the iron atoms have an oxidation state of +3, and one has +2. The average oxidation state is calculated as (2*3 + 1*2)/3 = +8/3.

12. Q12Hard

    Which of the following elements exhibits the **highest oxidation state** in its compounds?

    • A.Iron (Fe)
    • B.Copper (Cu)
    • C.Manganese (Mn)
    • D.Zinc (Zn)
    Answer: Manganese (Mn)

    Explanation: Manganese can exhibit oxidation states ranging from -3 to +7, with +7 being the highest oxidation state in its compounds like Mn₂O₇.

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