Chapter 6 Combustion and Flame mcqs & importantb questions science | class 8th

MCQ Questions for Class 8 Science: Ch 6 Combustion and Flame

1. Fuel may be

(a) Solid only

(b) Solid,Liquid or gas

(c) Liquid only

(d) Gas only

► (b) Solid,Liquid or gas

2. Which of the following has the characteristics of a good fuel?

(a) Coke

(b) Butane

(c) Coal

(d) Kerosene

► (b) Butane

3. Combustion is a _____ chemical reaction:

(a) volatile

(b) exothermic

(c) endothermic

(d) none of the above

► (b) exothermic

4. The substances which give heat and light after combustion are called

(a) flame

(b) fuel

(c) combustion

(d) none of these

► (b) fuel

5. Cutting trees at large scale leads to :

(a) deforestation

(b) afforestation

(c) reforestation

(d) both deforestation & afforestation

► (a) deforestation

6. What kind of reaction is combustion?

(a) Reduction

(b) Redox

(c) Substitution

(d) Oxidation

► (d) Oxidation

7. Substance that burns in oxygen to produce heat and light is called :

(a) renewable

(b) non combustible

(c) combustible

(d) limitless

► (c) combustible

8. If a glass plate/slide is held into the luminous part of candle flame we see a circular blackish ring that represents:

(a) unburnt carbon particles

(b) formation of coal

(c) burnt carbon particles

(d) Both burnt carbon particles & formation of coal

► (a) unburnt carbon particles

9. Burning of LPG is an example of :

(a) slow combustion

(b) spontaneous combustion

(c) Both slow combustion & spontaneous combustion

(d) rapid combustion

► (d) rapid combustion

10. SI unit of the calorific value of a fuel is :-

(a) KJ/kg

(b) KW/kg

(c) N/kg

(d) KJ/g

► (a) KJ/kg

11. Burning of charcoal in a closed room will produce

(a) carbon dioxide

(b) nitrogen dioxide

(c) carbon monoxide

(d) all of these

► (c) carbon monoxide

12. Which of the following is an example of rapid combustion?

(a) Candle

(b) Cracker

(c) White phosphorus

(d) Sulphur

► (a) Candle

13. The gas which supports combustion of coal is :

(a) carbon dioxide

(b) oxygen

(c) nitrogen

(d) hydrogen

► (b) oxygen

14. Amount of heat energy produced on complete combustion of 1kg of fuel is called :

(a) energy value

(b) combustion value

(c) heat value

(d) calorific value

► (d) calorific value

15. Combustion is a

(a) chemical process

(b) physical process

(c) both of these processes

(d) none of these processes

► (a) chemical process

16. A material that burns is one that can combine quickly with :

(a) hydrogen

(b) oxygen

(c) carbon

(d) water

► (b) oxygen

17. Water works as a fire extinguisher by removing :-

(a) source of combustible substance

(b) heat

(c) oxygen

(d) both oxygen & heat

► (d) both oxygen & heat

18. What is the lowest temperature at which a substance starts burning called?

(a) Minimum temperature

(b) Maximum temperature

(c) Boiling temperature

(d) Ignition temperature

► (d) Ignition temperature

19. It is dangerous to extinguish fire caused by an electric short circuit with the use of :

(a) sand

(b) carbon dioxide

(c) water

(d) carbon monoxide

► (c) water

20. Substance that does not burn in air is :

(a) sand

(b) kerosene

(c) wood

(d) diesel

► (a) sand

21. No external heat is required to start :

(a) simultaneous combustion

(b) spontaneous combustion

(c) splendid combustion

(d) spreading fire combustion

► (b) spontaneous combustion

22. CNG and LPG are the examples of

(a) solid fuels

(b) liquid fuels

(c) gaseous fuels

(d) they are not fuels

► (c) gaseous fuels

23. Which of the following is a non- combustible substance?

(a) Coke

(b) Diamond

(c) Coal

(d) Wood

► (b) Diamond

24. The products of combustion are

(a) carbon dioxide and water

(b) oxygen and water

(c) only carbon dioxide

(d) only oxygen

► (a) carbon dioxide and water

Class 8 Science Chapter 6 Extra Questions and Answers Combustion and Flame

Extra Questions for Class 8 Science Chapter 6 Combustion and Flame with Answers Solutions

Combustion and Flame Class 8 Extra Questions Very Short Answer Type

Question 1.
Name the most common fuel used in homes.
Answer:
Liquefied Petroleum Gas. (LPG)

Question 2.
Name the most common fire extinguisher.
Answer:
Water

Question 3.
What are the states in which a fuel may exist?
Answer:
A fual may exist in solid, liquid or gaseous state.

Question 4.
ame any two combustible substances.
Answer:
Charcoal, wood

Question 5.
Does magnesium produce heat and light during its combustion?
Answer:
Yes, it does.

Question 6.
What acts as a fuel for our body?
Answer:
Food

Question 7.
Give two examples of non-combustible substances.
Answer:
Water, sand

Question 8.
How are heat and light produced in the sun?
Answer:
In the sun, heat and light are produced by nuclear reactions.

Question 9.
Where were matchsticks first used?
Answer:
Egypt

Question 10.
What are the three essential requirements for combustion?
Answer:
Fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature).

Question 11.
What is the ignition temperature of phosphorus?
Answer:
25°C

Question 12.
What is the colour of an LPG flame?
Answer:
Blue

Question 13.
What type of process is combustion?
Answer:
A chemical process

Question 14.
Name an ideal fuel.
Answer:
Compressed Natural Gas (CNG)

Question 15.
What is the composition of the head of a matchstick?
Answer:
Antimony trisulphide and potassium chlorate.

Question 16.
Which part of a flame does a goldsmith blow for melting gold and silver?
Answer:
The goldsmith blows the outermost zone of a flame for melting gold and silver.

Question 17.
What is the unit for expressing the calorific value of a fuel?
Answer:
Kilojoules per kilogram (kJ/kg)

Question 18.
Comparing the calorific values of coal and petrol, state which fuel is better.
Answer:
The calorific value of coal is about 25,000 – 33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is better tuel.

Question 19.
What is deforestation?
Answer:
The cutting down of trees on a large scale is termed as deforestation.

Question 20.
Give any two examples of carbon fuels.
Answer:
Coal, petroleum

Combustion and Flame Class 8 Extra Questions Short Answer Type

Question 1.
What does magnesium burn to form?
Answer:
Magnesium burns to form magnesium oxide and produces heat and light.

Question 2.
What does coal produce during its combustion?
Answer:
Coal produces carbon dioxide, heat and light during its combustion.

Question 3.
What is combustion?
Answer:
Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Question 4.
Define the ignition temperature of a fuel.
Answer:
The lowest temperature at which a fuel catches fire is called its ignition temperature.

Question 5.
How does a matchstick catch fire?
Answer:
By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.

Question 6.
Why is sodium kept immersed in kerosene?
Answer:
Sodium has very low ignition temperature, i.e., it catches fire on coming in contact with air, so it is kept in kerosene.

Question 7.
What are combustible and non-combustible substances?
Answer:
Substances which undergo combustion are said to be combustible, whereas non-combustible substances are those which don’t burn.

Question 8.
What are inflammable substances? Give examples.
Answer:
The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances; e.g., LPG, petrol, alcohol, etc.

Question 9.
What is rapid combustion?
Answer:
When a substance burns instantly and produces a huge amount of heat and light, the combustion is called rapid combustion; e.g., the instant burning of LPG in a gas stove.

Question 10.
Define spontaneous combustion.
Answer:
A type of combustion in which the substance suddenly catches fire without the supply of heat or friction externally is called spontaneous combustion; e.g., forest fires.

Question 11.
Define explosion.
Answer:
A type of combustion during which a huge amount of heat and light is evolved with a boom, along with the production of gas, is known as explosion; e.g., the exploding of fireworks, i.e., crackers, etc.

Question 12.
What is flame?
Answer:
Flame is a region where the burning or combustion of gaseous substances take place.

Question 13.
Define fuel.
Answer:
Those substances which provide energy on burning are called ‘fuels’; e.g., coal, petroleum, LPG, etc.

Question 14.
Give two examples each of solid fuels, liquid fuels and gaseous fuels.
Answer:

• Solid fuels – Wood, cow dung, etc.
• Liquid fuels – Kerosene, petrol, etc.
• Gaseous fuels – Hydrogen, methane, etc.

Question 15.
Give two examples of fuels that are used to generate electricity.
Answer:
Two examples of fuels that are used to generate electricity are petrochemicals and coal.

Question 16.
Define calorific value.
Answer:
The amount of heat produced on burning one kilogram of fuel completely is called its calorific value.

Question 17.
60 kg of fuel was completely burnt for an experiment. The amount of heat energy was found to be 1,80,000 kJ. Calculate the calorific value of the fuel.
Answer:
Amount of fuel burnt = 60 kg
Amount of heat produced = 1,80,000 kJ

∴ Calorific value of the fuel is 3,000 kJ/kg.

Question 18.
Define dark zone of a flame.
Answer:
The innermost zone of a flame around the wick is called its dark zone. It is the least hottest zone comparatively to other.

Question 19.
Name the colours of the flames of following substances:
Barium, arsenic, sodium, magnesium
Answer:

Name of the substance	Colour of its flame
Barium	Pale/Apple green
Arsenic	Blue
Sodium	Yellow
Magnesium	White

Question 20.
Mention any three characteristics of a good fuel.
Answer:
Any three characteristics of a good fuel are following:

• It has high calorific value.
• It is very easy to transport.
• It is cheap, affordable and economic.

Question 21.
What is global warming?
Answer:
An increase in the average temperature of the earth’s atmosphere, especially a sustained increase that causes climatic changes, is termed as ‘global warming’.