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#10 MCQs on Electrochemistry (Grade 12)
Answers and explanations are provided.
# 1. What is the oxidation number of oxygen in KO₂ (superoxide)?
A) –2
B) –1
C) –1/2
D) +1
Answer: C) –1/2
Explanation: Rule 3 states oxygen in superoxides (e.g., KO₂) has an oxidation state of –1/2.
# 2. In the reaction: Mg(s) + 2HCl → MgCl₂(aq) + H₂(g), which species is oxidized?
A) Mg
B) H⁺
C) Cl⁻
D) H₂
Answer: A) Mg
Explanation: Mg loses electrons (oxidation: 0 → +2). H⁺ is reduced (gain electrons).
#3. In electrolytic conduction, what causes the increase in conductivity with temperature?
A) Delocalized electrons
B) Enhanced ionic mobility
C) Decomposition of ions
D) Reduced electrode resistance
Answer: B) Enhanced ionic mobility
Explanation: Electrolytic conductivity increases due to higher ionic mobility at elevated temperatures.
#4. During electrolysis of CuSO₄ using inert electrodes, which ion is discharged at the anode?
A) Cu²⁺
B) SO₄²⁻
C) OH⁻
D) O²⁻
Answer: C) OH⁻
Explanation: OH⁻ ions (from water) are lower in the electrochemicalL series than SO₄²⁻, so they oxidize to O₂ at the anode.
#5. What is the primary difference between metallic and electrolytic conduction?
A) Metallic conduction involves ions, while electrolytic involves electrons.
B) Metallic conduction involves electrons, while electrolytic involves ions.
C) Both involve ions.
D) Both involve electrons.
Answer: B) Metallic conduction involves electrons, while electrolytic involves ions.
#6. Which factor does NOT affect preferential discharge during electrolysis?
A) Electrode material
B) Ion concentration
C) Temperature of the solution
D) Position in the electrochemical series
Answer: C) Temperature of the solution
Explanation: Preferential discharge depends on ion position, concentration, and electrode nature, not temperature.
#7. In the electrolysis of brine (concentrated NaCl), what forms at the cathode?
A) Cl₂
B) H₂
C) O₂
D) Na
Answer: B) H₂
Explanation: H⁺ (from water) is reduced to H₂ at the cathode due to high Cl⁻ concentration favoring Cl₂ at the anode.
#8. Faraday’s first law relates mass deposited to:
A) Voltage
B) Current and time
C) Electrode surface area
D) Ion charge
Answer: B) Current and time
#9. Which metal is extracted via electrolysis of its molten oxide?
A) Iron
B) Copper
C) Aluminum
D) Zinc
Answer: C) Aluminum
Explanation: Al is extracted from molten Al₂O₃ (Hall-Héroult process).
# 10. In electroplating, the object to be plated acts as the:
A) Anode
B) Cathode
C) Electrolyte
D) Salt bridge
Answer: B) Cathode
Explanation: The metal to be plated is the cathode, where reduction (deposition) occurs.
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