CBSE Class 8 Science Exemplar Chapter 6: Combustion and Flame NCERT Solutions

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NCERT Solutions PDF Class 8 PDF

This chapter delves into the fundamental concepts of combustion and flame, crucial for understanding energy production and safety. The NCERT Solutions for Class 8 Science Exemplar Chapter 6 cover key topics such as identifying combustible and non-combustible substances, understanding the process of combustion, and the factors affecting it. It explains the concept of calorific value and its importance in fuel selection, along with the characteristics of a flame and the different zones within it. The solutions also address the conditions necessary for combustion and methods to control fire. These solutions are designed to provide clear, step-by-step explanations, helping students grasp the scientific principles involved and prepare effectively for their examinations.

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Quick info

BoardCBSE
ClassClass 8
SubjectScience Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 6

Chapter summary

Chapter 6 of the CBSE Class 8 Science Exemplar focuses on Combustion and Flame. The NCERT Solutions provided here explain the definition of combustible substances, differentiate them from non-combustible ones, and discuss the calorific value of fuels. It also covers the process of burning, the nature of flames, and the conditions required for combustion. The solutions clarify why certain substances burn and others do not, and how flames are produced.

Learning outcomes

  • Define and identify combustible and non-combustible substances.
  • Understand the concept of calorific value and compare fuels based on it.
  • Explain the process of combustion and the conditions required for it.
  • Describe the characteristics of a flame and its different zones.
  • Identify substances that burn with or without a flame.
  • Explain why a flame extinguishes due to lack of oxygen.

Topics covered

Paper topics

  • Combustion
  • Combustible substances
  • Non-combustible substances
  • Calorific value
  • Fuel
  • Flame
  • Conditions for combustion
  • Magnesium burning
  • Extinguishing flames

Important topics

  • Definition and examples of combustible and non-combustible substances
  • Understanding calorific value
  • Conditions necessary for combustion
  • Why flames extinguish

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Questions and Solutions

Multiple Choice Questions - 1

1. A substance which reacts with oxygen giving heat is called a combustible substance. Which, one of the following is a combustible substance?
  1. iron nail
  2. glass
  3. stone piece
  4. wood
Solution: The correct option is (d) wood. A combustible substance is one that readily burns in the presence of oxygen, releasing heat. While iron nails, glass, and stone pieces are generally non-combustible under normal conditions, wood burns easily in air, making it a combustible substance.

Multiple Choice Questions - 2

2. Which one of the following has the highest calorific value?
  1. kerosene
  2. biogas
  3. LPG
  4. petrol
Solution: The correct option is (c) LPG. Calorific value measures the amount of heat produced when a unit mass of a fuel is burnt completely. LPG has a high calorific value, typically around 55,000 kJ/kg, which is higher than that of kerosene, biogas, and petrol, indicating it is a more efficient fuel in terms of heat output per unit mass.

Multiple Choice Questions - 3

3. Magnesium ribbon on burning in air produces
  1. magnesium oxide, water and light
  2. magnesium oxide and heat
  3. magnesium oxide, heat and light
  4. magnesium oxide, water and heat
Solution: The correct option is (c) magnesium oxide, heat and light. When magnesium ribbon burns in air, it undergoes a chemical reaction with oxygen. This reaction produces magnesium oxide (MgO) as a solid residue, and it releases a significant amount of energy in the form of both heat and light. The chemical equation for this reaction is approximately 2Mg + O_2 \longrightarrow 2MgO, accompanied by the release of energy.

Multiple Choice Questions - 4

4. Which of the following is not a combustible substance?
  1. camphor
  2. glass
  3. straw
  4. alcohol
Solution: The correct option is (b) glass. A combustible substance is one that can burn in air. Camphor, straw, and alcohol are all combustible materials. Glass, however, is a non-combustible substance; it does not burn in air under normal conditions.

Multiple Choice Questions - 5

5. The substance that does not burn with flame is
  1. LPG
  2. camphor
  3. dry grass
  4. charcoal
Solution: The correct option is (d) charcoal. Substances like LPG, camphor, and dry grass typically burn with a visible flame. Charcoal, on the other hand, does not vaporize easily when heated. Instead of producing a flame, it burns with a glow, indicating combustion is occurring without the formation of a distinct flame.

Multiple Choice Questions - 6

6. On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of nonavailability of
  1. oxygen
  2. water vapours
  3. carbon dioxide
  4. wax
Solution: The correct option is (a) oxygen. Combustion is a chemical process that requires fuel, a supporter of combustion (usually oxygen), and heat. When an inverted tumbler is placed over a burning candle, it traps the air inside. As the candle burns, it consumes the available oxygen. Once the oxygen level drops below a certain point, the flame cannot be sustained and extinguishes.

Common mistakes

  • Confusing combustible and non-combustible substances.
  • Incorrectly identifying substances that burn with or without a flame.
  • Misunderstanding the role of oxygen in combustion.
  • Not differentiating between heat produced and calorific value.

Revision tips

  • Focus on understanding the definitions of key terms like 'combustible substance' and 'calorific value'.
  • Review the examples provided for combustible and non-combustible materials.
  • Pay attention to the conditions necessary for combustion and why they are important.
  • Visualize the process of a flame extinguishing due to lack of oxygen.

Practice MCQs

Q1. Which of the following substances is considered combustible?

Q2. Which fuel has the highest calorific value among the given options?

Q3. When magnesium ribbon burns in air, what are the products formed?

Q4. Which of the following is NOT a combustible substance?

Q5. A substance that does not burn with a visible flame, but instead glows, is:

Q6. Why does a candle flame extinguish when an inverted tumbler is placed over it?

Frequently asked questions

What is a combustible substance according to CBSE Class 8 Science?

A combustible substance is defined as a material that reacts with oxygen, usually producing heat and light, and is capable of burning. Examples include wood, LPG, and camphor.

What does 'calorific value' mean in the context of fuels?

Calorific value represents the amount of heat energy released when a unit mass or volume of a fuel is completely burned. A higher calorific value means more heat is produced.

Why is oxygen essential for combustion?

Oxygen acts as an oxidant in the combustion process. Without a sufficient supply of oxygen, a substance cannot burn or sustain a flame.

Can glass burn?

No, glass is a non-combustible substance. It does not react with oxygen to produce heat and light under normal conditions.

How do these NCERT Solutions help with exam preparation?

These solutions provide clear, rewritten explanations for each question, helping students understand the concepts of combustion and flame thoroughly and reinforcing their knowledge for exams.

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