Chemical Effects of Electric Current Part 3: MCQs (Q51–Q75)
⚡ Chemical Effects of Electric Current – MCQs for Class 8 Science
Part 3: Q51–Q75
Q51. Electroplating of iron with zinc is called:
A) Alloying
B) Galvanization
C) Electrorefining
D) Oxidation
✅ Correct Answer: B) Galvanization
Explanation:
- B) ✔ Galvanization = coating iron with zinc to prevent rust.
- A) Alloying = mixing metals.
- C) Electrorefining = purifying metals.
- D) Oxidation = chemical reaction with oxygen.
Q52. In an electrolytic cell, the flow of current inside the electrolyte is due to:
A) Free electrons
B) Ions
C) Neutrons
D) Protons
✅ Correct Answer: B) Ions
Explanation:
- B) ✔ Positive and negative ions carry current in liquids.
- A) Free electrons conduct in metals, not in solutions.
- C, D) Do not move freely in solution.
Q53. The main product at the cathode during electrolysis of brine is:
A) Oxygen
B) Chlorine
C) Hydrogen
D) Sodium hydroxide
✅ Correct Answer: C) Hydrogen
Explanation:
- C) ✔ H⁺ ions get reduced at cathode → hydrogen gas.
- B) Chlorine is released at anode.
- D) NaOH remains in solution.
Q54. Electroplating of chromium is used because chromium is:
A) Heavy and strong
B) Hard and corrosion-resistant
C) Soft and shiny
D) Very cheap
✅ Correct Answer: B) Hard and corrosion-resistant
Explanation:
- B) ✔ Chromium is hard, shiny, and resists corrosion.
Q55. During electrolysis of copper sulphate, the colour of solution fades because:
A) Copper ions are deposited on cathode
B) Water evaporates
C) Electrolyte gets heated
D) Sulphur separates
✅ Correct Answer: A) Copper ions are deposited on cathode
Explanation:
- A) ✔ Cu²⁺ ions decrease from solution → colour fades.
Q56. Which one of the following is NOT a chemical effect of current?
A) Bubbles formation at electrodes
B) Deposition of metal on electrodes
C) Change in solution colour
D) Heating of filament in bulb
✅ Correct Answer: D) Heating of filament in bulb
Explanation:
- D) ✔ This is heating effect, not chemical effect.
Q57. Why is electroplating done in industry?
A) To reduce cost
B) To make articles attractive and corrosion-resistant
C) To increase weight
D) To make them magnetic
✅ Correct Answer: B) To make articles attractive and corrosion-resistant
Explanation:
- B) ✔ Electroplating improves appearance and durability.
Q58. Which of the following is a conductor?
A) Vinegar
B) Alcohol
C) Petrol
D) Kerosene
✅ Correct Answer: A) Vinegar
Explanation:
- A) ✔ Vinegar contains acetic acid → provides ions.
Q59. Which non-metal is a good conductor of electricity?
A) Sulphur
B) Graphite
C) Phosphorus
D) Iodine
✅ Correct Answer: B) Graphite
Explanation:
- B) ✔ Graphite (carbon allotrope) conducts due to free electrons.
Q60. In electroplating of silver on copper, the silver electrode is:
A) Cathode
B) Anode
C) Both
D) None
✅ Correct Answer: B) Anode
Explanation:
- B) ✔ Silver dissolves from anode and deposits on copper at cathode.
Q61. Which type of current is used in electroplating?
A) Alternating current (AC)
B) Direct current (DC)
C) High voltage current
D) Any current
✅ Correct Answer: B) Direct current (DC)
Explanation:
- B) ✔ DC ensures ions move in fixed direction → proper deposition.
Q62. When acidified water undergoes electrolysis, oxygen is released at:
A) Cathode
B) Anode
C) Both electrodes
D) None
✅ Correct Answer: B) Anode
Explanation:
- B) ✔ Negative ions (OH⁻) move to anode → O₂ gas released.
Q63. Which is NOT an electrolyte?
A) Sodium chloride solution
B) Copper sulphate solution
C) Sugar solution
D) Lemon juice
✅ Correct Answer: C) Sugar solution
Explanation:
- C) ✔ Sugar doesn’t ionize → no conductivity.
Q64. Which gas is released at the anode during electrolysis of brine?
A) Oxygen
B) Hydrogen
C) Chlorine
D) Nitrogen
✅ Correct Answer: C) Chlorine
Explanation:
- C) ✔ Chloride ions → Cl₂ at anode.
Q65. In which case will the bulb glow brightest in a tester?
A) Vinegar
B) Tap water
C) Distilled water
D) Kerosene
✅ Correct Answer: B) Tap water
Explanation:
- B) ✔ Contains salts → better conductor → more current.
Q66. The release of bubbles during electrolysis is due to:
A) Deposition of metal
B) Liberation of gases
C) Movement of ions
D) Evaporation
✅ Correct Answer: B) Liberation of gases
Explanation:
- B) ✔ H₂ and O₂ gases form bubbles.
Q67. During electrolysis of copper sulphate using copper electrodes, the solution concentration:
A) Increases
B) Decreases
C) Remains constant
D) Disappears
✅ Correct Answer: C) Remains constant
Explanation:
- C) ✔ Copper dissolves at anode = copper deposited at cathode → balanced.
Q68. Which of the following is not a good conductor of electricity?
A) Salt solution
B) Lemon juice
C) Alcohol
D) Tap water
✅ Correct Answer: C) Alcohol
Explanation:
- C) ✔ Alcohol has no free ions → poor conductor.
Q69. The layer deposited on iron cans to prevent corrosion is:
A) Chromium
B) Tin
C) Zinc
D) Copper
✅ Correct Answer: B) Tin
Explanation:
- B) ✔ Food cans are tin-plated to prevent rust.
Q70. During electrolysis, which electrode attracts cations?
A) Anode
B) Cathode
C) Both
D) None
✅ Correct Answer: B) Cathode
Explanation:
- B) ✔ Cathode = negative → attracts positive ions.
Q71. Which statement about electrolysis is correct?
A) It requires AC current
B) It requires DC current
C) It works without electrodes
D) It happens in pure water only
✅ Correct Answer: B) It requires DC current
Explanation:
- B) ✔ DC ensures unidirectional flow for ion deposition.
Q72. The bubbles seen at electrodes during electrolysis of water are of:
A) H₂ at anode and O₂ at cathode
B) O₂ at anode and H₂ at cathode
C) Both H₂ at both electrodes
D) Only O₂
✅ Correct Answer: B) O₂ at anode and H₂ at cathode
Explanation:
- B) ✔ Correct placement of gases.
Q73. Which factor affects electroplating rate?
A) Temperature
B) Voltage of current
C) Concentration of electrolyte
D) All of these
✅ Correct Answer: D) All of these
Explanation:
- D) ✔ All influence deposition speed and thickness.
Q74. Which electrolyte is used for electroplating iron with nickel?
A) Nickel sulphate solution
B) Copper sulphate solution
C) Zinc sulphate solution
D) Sodium chloride solution
✅ Correct Answer: A) Nickel sulphate solution
Explanation:
- A) ✔ Provides Ni²⁺ ions for deposition.
Q75. What is the role of anode in electroplating?
A) Deposition surface
B) Source of metal ions
C) Decorative layer
D) Prevents corrosion
✅ Correct Answer: B) Source of metal ions
Explanation:
- B) ✔ Metal dissolves from anode and deposits on cathode.
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