🔥 CBSE · Class 8 · Science · Chapter 6

Combustion
and Flame

Complete chapter resources for CBSE Class 8 Science — types of combustion, conditions for burning, zones of a candle flame, fuels and calorific value, fire control methods, and sample questions.

3Topics

3–5Board marks

8Sample questions

3PYQ included

Free for independent teachers · No credit card required

Key Concepts — Chapter 6

Combustion: Fuel + O₂ → CO₂ + H₂O + Heat + Light
Ignition temp: Minimum temp needed to catch fire
Calorific value: Heat energy per kg of fuel (kJ/kg)
Flame zones: Dark (innermost) → Luminous → Blue (hottest)
Fire triangle: Fuel + Heat + Oxygen — remove one to extinguish
Global warming: Excess CO₂ from combustion traps heat

Chapter Overview

What this chapter covers

Combustion is a chemical process in which a substance reacts with oxygen to produce heat and light. For combustion to occur, three conditions must be met simultaneously: the presence of a combustible substance (fuel), the availability of a supporter of combustion (oxygen), and the attainment of the ignition temperature — the minimum temperature at which a substance starts to burn. This forms the basis of the "fire triangle," and understanding it is key to fire prevention and firefighting.

The chapter classifies combustion into three types: rapid combustion (burning quickly with heat and light, e.g., LPG), spontaneous combustion (burning without an external heat source when ignition temperature is reached on its own, e.g., white phosphorus), and explosion (sudden, loud combustion due to rapid burning, e.g., crackers). Students also study a candle flame in detail — its three zones (dark innermost, luminous middle, and outermost blue zone) — and why the outermost zone is the hottest.

A major focus of the chapter is fuels and their properties: calorific value (energy released per kg of fuel), ideal fuel characteristics, and the environmental consequences of burning fuels, including acid rain and global warming due to excess CO₂ and SO₂ emissions. Fire extinguishers — and the science behind how they work by removing one element of the fire triangle — are also covered, making this chapter practical as well as conceptual.

Topics

What's inside Chapter 6

As per NCERT Class 8 Science (CBSE syllabus)

Topic 1

Combustion — Conditions and Types

Definition of combustion, the fire triangle (fuel, heat, oxygen). Types: rapid combustion, spontaneous combustion, and explosion. Concept of ignition temperature and inflammable substances.

Topic 2

Flame and Zones of a Candle Flame

Structure of a flame — three zones (dark innermost zone, luminous middle zone, outermost non-luminous blue zone). Why the outermost zone is the hottest. Substances that produce a flame vs those that do not (e.g., charcoal).

Topic 3

Fuels, Calorific Value & Environmental Impact

Definition and measurement of calorific value (kJ/kg). Properties of an ideal fuel. Comparison of common fuels (wood, coal, LPG, CNG). Harmful effects: CO₂ and global warming, SO₂ and acid rain, unburnt carbon particles and respiratory hazards.

Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on

Ch 3 · Synthetic Fibres and Plastics

Concept of flammability and heat behaviour of materials

Class 7 · Ch 6 · Physical & Chemical Changes

Combustion as an irreversible chemical change producing new substances

Chapter 6 Combustion
and Flame

Leads to

Ch 7 · Conservation of Plants and Animals

Forest fires, deforestation, and environmental consequences of burning

Class 10 · Ch 1 · Chemical Reactions & Equations

Balanced combustion equations, oxidation reactions, exothermic processes

Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 8 Science school examination papers.

Question type	Marks	Typical count	What's usually tested
MCQ / Fill in the blank	1	1–2	Type of combustion, ignition temperature, hottest zone of flame
Very Short Answer	1–2	1	Define calorific value, name types of combustion, fire triangle elements
Short Answer	2–3	1	Explain zones of candle flame, conditions for combustion, or fire control methods
Long Answer / Descriptive	4–5	0–1	Compare fuels, effects of burning on environment, ideal fuel properties
Total (approximate)	3–5	2–4	Weightage varies across school paper sets and terms

Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 8 Science Chapter 6. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ

Which zone of a candle flame is the hottest? (a) Dark innermost zone (b) Luminous middle zone (c) Outermost blue zone (d) All zones have equal temperature

Q2 Easy 1 mark Short Answer

Define ignition temperature.

Q3 Medium 2 marks Short Answer

Name and describe the three types of combustion with one example each.

Q4 Medium 2 marks Short Answer

What is calorific value? If LPG has a calorific value of 55,000 kJ/kg and wood has 17,000 kJ/kg, which is a better fuel and why?

Q5 Medium 3 marks Short Answer

Draw and label the three zones of a candle flame. Explain what happens in each zone during the burning of a candle.

Q6 Hard 3 marks Short Answer

A firefighter uses a CO₂ extinguisher to put out a fire. (a) Name the three elements of the fire triangle. (b) Which element does the CO₂ extinguisher remove? (c) Why is water NOT used on electrical fires?

Q7 Hard 4 marks Word Problem

Rohan's school kitchen uses wood as fuel. The calorific value of wood is 17,000 kJ/kg. If the kitchen burns 6 kg of wood daily, calculate the total heat energy produced in one week. Also suggest TWO reasons why the school should switch to LPG (calorific value 55,000 kJ/kg) as a fuel.

Q8 Hard 5 marks Descriptive

Burning of fossil fuels is a major cause of environmental problems. (i) Name TWO harmful gases produced when coal burns. (ii) How does excess CO₂ in the atmosphere cause global warming? (iii) Which gas causes acid rain, and how does acid rain affect living organisms? (iv) Suggest TWO ways to reduce the harmful effects of burning fossil fuels.

Generate a full paper with answer key →

MarksZen AI creates a complete question paper with answer key in under 2 minutes.

Previous Year Questions

From CBSE school examinations

Representative questions from past Class 8 Science annual and periodic test papers — Combustion and Flame chapter.

Board 20223 marks

Explain why: (a) Water is not used to control fire caused by burning oil. (b) LPG is considered a better fuel than wood. (c) Goldsmiths use the outermost zone of a candle flame for melting gold. (CBSE Annual Exam 2022)

Board 20232 marks

What is spontaneous combustion? Give one example of a substance that undergoes spontaneous combustion, and state the condition under which it occurs. (CBSE Periodic Test 2023)

Board 20204 marks

Describe the structure of a candle flame with the help of a labelled diagram. Explain what occurs in each zone and state which zone is used in laboratory experiments for heating, giving a reason. (CBSE Annual Exam 2020)

For Teachers

Create a board-aligned
question paper in 2 minutes.

Pick chapter, set the question-type mix and total marks — MarksZen AI generates the full paper with answer key. CBSE, ICSE, and all State Boards supported.

All 3 topics of this chapter
MCQ + short answer + descriptive
Answer key included
PDF export ready

FAQ

Questions teachers ask

How many marks does Combustion and Flame carry in the CBSE Class 8 Science exam? +

Combustion and Flame typically contributes 3–5 marks in Class 8 Science school examinations. Questions usually include one 1-mark definition or MCQ, one 2-mark short answer (types of combustion or zones of flame), and occasionally a 3-mark descriptive question on fire control or fuel comparison. The exact marks vary by school paper, but the chapter is high-yield for short-answer questions.

What are the three conditions necessary for combustion? +

The three essential conditions for combustion are: (1) presence of a combustible substance (fuel), (2) supply of a supporter of combustion (usually oxygen from air), and (3) attainment of the ignition temperature — the minimum temperature at which a substance catches fire. Removing any one of these three conditions extinguishes or prevents a fire, which is the principle behind all fire-fighting methods.

What are the different zones of a candle flame and what happens in each zone? +

A candle flame has three distinct zones. The innermost dark zone contains unburnt wax vapour and is the coolest part. The middle luminous (yellow) zone has partial combustion of carbon particles that glow, making this the brightest region. The outermost blue zone has complete combustion with full access to oxygen and is the hottest part of the flame. Goldsmiths use the outermost zone for metalwork because of its high temperature.

What is calorific value and why is it important for comparing fuels? +

Calorific value is the amount of heat energy produced when 1 kg of a fuel is completely burnt. It is measured in kJ/kg (kilojoules per kilogram). A higher calorific value means a fuel releases more energy per unit mass, making it more efficient. For example, LPG has a calorific value of about 55,000 kJ/kg, which is much higher than wood (~17,000 kJ/kg), which is why LPG is preferred as a cooking fuel.

How do I generate a custom question paper for Combustion and Flame using MarksZen? +

Sign up for a free MarksZen account, choose CBSE Class 8 Science, select Chapter 6 (Combustion and Flame), set your preferred question-type mix (MCQ, short answer, descriptive) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.

Combustionand Flame