Class 8 Science MCQ | Chemical Effects of Electric Current, Electroplating, Conductors & LED

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Practice Class 8 Science MCQ Questions with Answers based on the latest NCERT syllabus. Learn about the chemical effects of electric current, electroplating, electrolysis, conductors, LED, and distilled water with original concept-based explanations, exam-focused notes, and NCERT-aligned content for CBSE and State Board students.

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Chapter Information

Subject: Science

Class: 8

Chapter: Chemical Effects of Electric Current

Question Type: Multiple Choice Questions (MCQs)

Difficulty Level: Easy to Moderate

Based On: Latest NCERT Syllabus

Introduction

Electric current can produce not only heating and magnetic effects but also chemical changes when it passes through certain conducting liquids. This phenomenon is known as the chemical effect of electric current. It has many practical applications, including electroplating, metal purification, and industrial manufacturing. This practice set helps students understand these concepts through original, NCERT-aligned explanations.

What You Will Learn

✔ Chemical effects of electric current

✔ Electrolysis of water

✔ Electroplating

✔ Conductors and insulators

✔ LED and distilled water

Why This Topic Is Important?

The chemical effects of electric current are widely used in industries for coating metals, manufacturing chemicals, and purifying metals. These concepts are frequently asked in CBSE, State Board, Olympiad, and scholarship examinations.

Exam Relevance

These questions are useful for:

✔ CBSE Exams

✔ State Board Exams

✔ School Tests

✔ Unit Tests

✔ Half-Yearly Exams

✔ Annual Exams

✔ Olympiad Preparation

✔ Scholarship Examinations

Q1. Which of the following is a good conductor of electricity?

A) Plastic

B) Copper

C) Rubber

D) Wood

Answer

Copper

Concept

Conductors allow electric current to pass through them easily.

Explanation

Copper has very low electrical resistance and is widely used for electrical wiring. Materials such as plastic, rubber, and dry wood are poor conductors and are commonly used as electrical insulators.

Exam Focus

Remember: Copper is one of the best conductors used in electrical circuits.

explanation:

1. Materials are classified as conductors and insulators.
2. Conductors allow electric current to pass through them easily.
3. Metals like copper, aluminium have free electrons that carry current.
4. Rubber, plastic, and wood do not allow current to pass easily (they are insulators).

Conclusion:
Copper is a good conductor of electricity.

Q2. Pure or distilled water is?

A) Good conductor

B) None of these

C) Poor conductor

D) Semiconductor

Answer

Poor conductor

Concept

Pure water contains very few ions, so it does not conduct electricity effectively.

Explanation

Distilled water is a poor conductor of electricity because it lacks dissolved salts and minerals. When impurities or salts are added, the number of ions increases, allowing electric current to flow more easily.

Exam Focus

Remember: Pure water is a poor conductor, while ordinary tap water conducts electricity due to dissolved salts.

explanation:

1. Pure (distilled) water does not contain dissolved salts or minerals.
2. Electric current flows through water only when ions (charged particles) are present.
3. Since distilled water has almost no ions, it cannot conduct electricity well.
4. Normal tap water conducts electricity because it contains dissolved impurities.

Conclusion:
Pure/distilled water is a poor conductor.

Q3. The process of depositing a layer of any desired metal on another material by means of electricity is called?

A) Electroplating

B) Galvanization

C) Electrolysis

D) Ionization

Answer

Electroplating

Concept

Electroplating uses electric current to deposit a thin layer of one metal onto another object.

Explanation

Electroplating improves the appearance, prevents corrosion, and increases the durability of metal objects. Common examples include silver-plated jewellery, chromium-plated taps, and gold-plated ornaments.

Exam Focus

Remember: Electroplating = Metal coating using electricity.

explanation:

1. When electric current is passed through a solution, chemical changes can occur.
2. In Electroplating, a thin layer of one metal is deposited on another material.
3. This is done to improve appearance, strength, or prevent rusting.
4. Example: Gold plating on jewellery, chromium plating on taps.

Conclusion:
This process is called Electroplating.

Q4. LED stands for?

A) Light Emitting Device

B) Light Emitter Diode

C) Low Energy Diode

D) Light Emitting Diode

Answer

Light Emitting Diode

Concept

An LED is an electronic device that emits light when electric current flows through it.

Explanation

LED (Light Emitting Diode) is widely used in electrical appliances, display panels, indicators, and testing circuits because it consumes less electricity and has a long operating life.

Exam FocusRemember: LED = Light Emitting Diode

explanation:

1. LED is an electronic component.
2. When electric current passes through it, it emits light.
3. It uses very low energy and lasts longer than bulbs.
4. LEDs are commonly used in TVs, indicators, and decorative lights.

Conclusion:
LED stands for Light Emitting Diode.

Q5. When an electric current is passed through acidified water, which gas is formed at the positive terminal (Anode)?

A) Hydrogen

B) Nitrogen

C) Oxygen

D) Carbon dioxide

Answer

Oxygen

Concept

Acidified water undergoes electrolysis when an electric current passes through it.

Explanation

During the electrolysis of acidified water:

• Oxygen gas is released at the positive electrode (anode).
• Hydrogen gas is released at the negative electrode (cathode).

This occurs because water molecules decompose into hydrogen and oxygen gases under the influence of electric current.

Exam Focus

Remember:

• Anode (+) → Oxygen
• Cathode (–) → Hydrogen

explanation:

1. Passing electricity through acidified water causes Electrolysis of water.
2. Water splits into two gases: Hydrogen (H₂) and Oxygen (O₂).
3. At the cathode (negative terminal) → Hydrogen gas is formed.
4. At the anode (positive terminal) → Oxygen gas is formed.

Conclusion:
Gas formed at the positive terminal (anode) is Oxygen.

Important Concepts

1. Chemical Effect of Electric Current

• Electric current can cause chemical reactions.
• Produces gases, metal deposits, or colour changes in solutions.

2. Electrolysis of Water

During electrolysis:

• Anode (+) → Oxygen gas
• Cathode (–) → Hydrogen gas

3. Electroplating

Uses:

• Prevents corrosion.
• Improves appearance.
• Increases durability.
• Reduces cost by coating cheaper metals.

Examples:

• Gold-plated jewellery
• Chromium-plated bicycle handlebars
• Silver-plated utensils

4. Conductors and Insulators

Good Conductors

• Copper
• Aluminium
• Silver

Poor Conductors (Insulators)

• Plastic
• Rubber
• Wood
• Glass

5. LED

• Full Form: Light Emitting Diode
• Low power consumption.
• Long lifespan.
• Used as indicators and display lights.

6. Distilled Water

• Pure water contains almost no dissolved ions.
• Poor conductor of electricity.
• Conductivity increases when salts or acids are dissolved.

Related Practice Questions

1. What is electroplating? Give two applications.
2. Why is acid added to water before electrolysis?
3. Why is copper widely used for electrical wiring?
4. Write the full form of LED.
5. Why is distilled water a poor conductor of electricity?

Mini Quiz Challenge

True or False

1. Oxygen is produced at the anode during electrolysis of acidified water.
2. Electroplating is used to coat one metal with another.
3. Copper is a good conductor of electricity.
4. LED stands for Light Emitting Diode.
5. Distilled water is a good conductor of electricity.

Exam Tips

✔ Remember which gases are produced at the anode and cathode.

✔ Do not confuse electrolysis with electroplating.

✔ Learn common examples of conductors and insulators.

✔ Memorize the full form of LED.

✔ Understand why dissolved salts make water conductive.

Quick Revision Notes

✔ Chemical effects occur when electric current passes through conducting liquids.

✔ Oxygen is produced at the anode.

✔ Hydrogen is produced at the cathode.

✔ Electroplating deposits a thin metal coating using electricity.

✔ Copper is a good conductor.

✔ LED = Light Emitting Diode.

✔ Distilled water is a poor conductor.

Common Mistakes Students Make

❌ Confusing the gases produced at the anode and cathode.

❌ Thinking electroplating and electrolysis are the same process.

❌ Assuming plastic conducts electricity.

❌ Writing an incorrect full form of LED.

❌ Believing distilled water conducts electricity like tap water.

Key Takeaways

• During electrolysis of acidified water, oxygen is produced at the anode and hydrogen at the cathode.
• Electroplating deposits a protective or decorative layer of metal using electric current.
• Copper is an excellent conductor of electricity and is widely used in electrical wiring.
• LED stands for Light Emitting Diode and is an energy-efficient light source.
• Distilled water is a poor conductor because it contains very few dissolved ions.

Conclusion

Understanding the chemical effects of electric current helps students explain many real-life applications, including electroplating, metal purification, and electrical testing. Regular MCQ practice strengthens conceptual understanding and improves confidence for school examinations and competitive tests.

FAQs

1. Which gas is produced at the anode during electrolysis of acidified water?

Oxygen gas is produced at the positive electrode (anode).

2. What is electroplating?

Electroplating is the process of depositing a thin layer of one metal onto another material using electric current.

3. Why is copper used for electrical wiring?

Copper has high electrical conductivity and low resistance, making it suitable for carrying electric current efficiently.

4. What is the full form of LED?

LED stands for Light Emitting Diode.

5. Why is distilled water a poor conductor of electricity?

Distilled water contains almost no dissolved ions, so it does not allow electric current to flow easily.

NCERT Reference

Book: NCERT Science Class 8

Chapter: Chapter 14 – Chemical Effects of Electric Current

Based On: Latest NCERT Curriculum (CBSE)

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