Study Important Questions for Class 8 Science Chapter 4 – Combustion and Flame - FREE PDF Download
Very Short Answer Questions: (1 Mark)
1. ________ do not produce flames but generate heat.
A. Kerosene
B. Oil
C. Petrol
D. Coal
Ans: D. Coal
2. Which of the following is the product of combustion?
A. Carbon dioxide and water
B. Oxygen and Water
C. Only Carbon Dioxide
D. Only Oxygen
Ans: A. Carbon Dioxide and Water
3. Which one of the following is a combustible substance?
A. Wood
B. Nail
C. Steel spoon
D. All of These
Ans: A. Wood
4. __________ is produced when a charcoal is burnt in a closed room?
A. carbon dioxide
B. Nitrogen Dioxide
C. Carbon Monoxide
D. All of These
Ans: C. Carbon Monoxide
5. What is used as fuel to run automobiles?
A. Petrol
B. Diesel
C. Kerosene
D. Both A and B
Ans: D. Both A and B
6. A good fuel is one which is ______________.
A. Cheap
B. Readily Available
C. Produces Large Amount of Heat
D. All of These
Ans: D. All of these
7. How many zones are there in the flame?
A. One
B. Three
C. Two
D. Four
Ans: B. Three
8. What are the requirements essential for producing fire?
Ans: Requirements for producing fire:
Fuel
Air (Oxygen)
Ignition Temperature
9. Charcoal burns in air to produce ______________, _______________ and ___________.
Ans: Carbon Dioxide, Heat and Light.
10. Name any one chemical substance which helps to put off the fire other than carbon dioxide.
Ans: Bicarbonates of sodium or potassium will help us to put off the fire.
11. In the Sun, heat and light are produced by ___________.
Ans: Nuclear Reaction.
12. Expand LPG.
Ans: Liquified Petroleum Gas
13. The lowest temperature at which a substance catches fire is called ___________.
Ans: Ignition Temperature
14. The unit of a calorific value of a fuel is _________________.
Ans: Kilojoules per Kilogram.
Short Answer Questions: (3 Marks)
15. Classify the following into combustible and non-combustible substances.
iron rod, wood, steel spoon, stone, newspaper, petrol
Ans:
16. Kerosene oil while burying gives flames on the other hand charcoal does not produce flames? Give a reason.
Ans: Only substances which vaporise during burning can produce flames such as kerosene whereas charcoal doesn’t vaporise when starting burning. Thus, charcoal doesn’t produce any flame.
17. If a fire breaks out in the petrol station, how does a fire extinguisher help to put off the fire?
Ans: A combination of liquid and gaseous carbon is used in fire extinguishers. Because carbon dioxide is heavier than oxygen, it blankets the fire. Thus, the fire is controlled because there is no contact between the fuel and the oxygen.
18. Petrol can be considered as a good fuel. Why?
Ans: Reasons petrol is considered a good fuel:
a. It is affordable.
b. It is easily available.
c. It has a high calorific value.
d. It is easy to transport.
e. It burns easily and produces more heat.
19. What will happen when a paper cup with water is heated?
Ans: When we heat a paper cup containing water, the water will absorb the heat of the flame. Hence, the ignition temperature of paper will not reach and it will not start burning easily.
20. Give four examples of inflammable substances.
Ans: Four inflammable substances:
a. Kerosene
b. Petrol
c. LPG
d. Diesel
21. How does combustion start in a matchstick?
Ans: Antimony trisulphide and potassium chlorate are found in the matchstick's head. The rubbing surface has powdered glass & red phosphorus. Red phosphorus is transformed to white phosphorus when the match is hit against the rubbing surface. This combines with the potassium chlorate in the matchstick head to provide enough heat to ignite antimony trisulphide and start the combustion process.
22. Define the following.
a. Combustion: Combustion is a chemical reaction in which a material combines with oxygen present in air to produce heat.
b. Fuel: Fuels are the substances which undergo combustion.
c. Calorific Value: The calorific value of a fuel is the quantity of heat energy produced when 1 kg of fuel is completely burned.
23. Why is it not advised to use water if an electrical equipment is on fire?
Ans: Water is a good conductor of electricity which increases the risk to the helpers. Therefore it is advised not to use water if there is any electrical equipment on fire.
24. Label the different zones of a candle flame.
Ans:
A – outer zone of complete combustion (Blue coloured)
B – Middle zone of partial combustion (yellow coloured)
C – Innermost zone of unburnt wax vapours (black coloured)
25. In an experiment, 1 kg of fuel was completely burnt. The heat produced was measured to be 9,000 kJ.
a. What will be the head produced for 7 kg of fuel?
Ans: If the heat produced for 1 kg of fuel is 9000 kJ.
Then heat produced for 7 kg is = 7 X 9000
= 63,000 kJ
b. Calculate the calorific value of the fuel.
Ans: Calorific value of the fuel = Amount of heat energy produced / weight of fuel burnt
= 63000/8 kJ/kg
= 9,000 kJ/kg
Long Answer Questions: (5 Marks)
26. List the characteristics of an ideal fuel.
Ans: Characteristics of an ideal fuel:
a. It should be affordable.
b. It should be easily available.
c. It should have high calorific value.
d. It should be easy to transport.
e. It should burn easily and produce more heat.
f. It should not leave any unwanted residue behind on burning.
g. It should be more environmentally friendly.
27. With the help of an experiment show that air is necessary for combustion.
Ans:
i. Take two lighted candles on a table.
ii. Put a glass chimney over one candle s in such a way that air can enter the chimney.
iii. On the other hand, put a chimney over another candle and place a glass plate over the chimney.
iv. We observe that the first candle continues to burn whereas flame in the second candle extinguishes.
This is because the air supply was cut off after placing the glass plate over the chimney and the candle was not able to burn in the absence of air. This shows that air (oxygen) is necessary for combustion.
28. Explain the different types of combustion with examples.
Ans: There are three different types of combustions:
a. Rapid Combustion: It's a form of combustion in which a substance burns quickly, releasing heat and light. Example: LPG.
b. Spontaneous Combustion: The sort of combustion in which a substance spontaneously erupts into flames without any apparent cause.
Example: Phosphorus. It burns in air at ambient temperature without igniting.
c. Explosion: When a substance is ignited, it undergoes a rapid reaction that produces heat, light, and sound. The reaction produces a significant amount of gas and heat, which is then released. This type of combustion is called an explosion.
Example: Bursting of firecrackers.
29. Explain in detail the harmful effect caused by burning of fuel.
Ans: Harmful effects of burning of fuels:
a. The carbon based wood, coal etc leaves unburnt substances which causes air pollution. They can be harmful for humans too, causing respiratory diseases.
b. Most of the fuel releases carbon dioxide on burning. This process slowly increases carbon content in the atmosphere leading to bigger problems like global warming.
c. Incomplete combustion of fuel can produce carbon monoxide instead of dioxide which when inhaled can rapidly combine with our blood and work as poison.
d. In a few cases sulphur dioxide is produced on burning of fuel which is harmful to both humans and the environment.
5 Important Topics of Class 8 Science Chapter 4 You Shouldn’t Miss!
Benefits of Class 8 Chapter 4 Science Important Questions
Clear Understanding of Concepts: Important questions help students understand key ideas about combustion and its types.
Enhanced Critical Thinking: These questions encourage students to think about how combustion works in everyday life.
Improved Retention of Information: Answering questions helps students remember important facts about combustion and flames.
Better Exam Preparation: Practising these questions prepares students for exams by showing them what to focus on.
Real-World Application: The questions connect what students learn to real-life situations, showing the importance of combustion.
Development of Safety Awareness: Important questions cover fire safety, helping students understand how to stay safe around flames.
Increased Confidence: Regular practice helps students feel more confident in their knowledge for tests and discussions.
Conclusion
The important questions for Class 8 Science Chapter 4, "Combustion and Flame," are essential for understanding key concepts about combustion and flames. They help students learn about different types of combustion and the importance of fire safety. Practising these questions improves exam readiness and connects what they learn to real-life situations. Overall, these questions enhance the learning experience and strengthen knowledge about combustion.
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FAQs on CBSE Class 8 Science Important Questions Chapter 4 - Combustion and Flame
1. How do Vedantu’s important questions help in understanding combustion and flame?
Important questions provide a focused way for students to learn about key concepts in combustion and flame. They guide students in identifying what to study and reinforce their understanding of the topic.
2. Why is it essential to practise Vedantu’s important questions for Class 8 Chapter 4?
Practising important questions is essential because it helps students review the main ideas and prepare effectively for exams. This practice can improve their confidence and performance.
3. What skills can students develop by answering important questions in this chapter?
By answering important questions, students can develop critical thinking skills as they analyse different scenarios related to combustion. They also improve their ability to explain concepts clearly.
4. How can important questions assist in exam preparation for Class 8 Science?
Important questions help students focus on essential topics and concepts that are likely to appear on exams. This focused preparation leads to a better understanding and readiness for the assessment.
5. What role do important questions play in retaining information about combustion?
Important questions promote active learning, which helps students remember key facts about combustion and flames more effectively. Regular practice reinforces their memory of these concepts.
6. How can students use important questions to check their understanding of the chapter?
Students can use important questions to test their knowledge and identify areas where they need more practice. This self-assessment helps them understand their strengths and weaknesses.
7. Can Vedantu’s important questions help in improving writing skills for exams?
Yes, practising important questions helps students organize their thoughts and present them. This practice can improve their writing skills, which is essential for written exams.
8. What types of important questions can students expect for Chapter 4 at Vedantu?
Students can expect a mix of theoretical questions, practical applications, and problem-solving questions related to combustion. This variety helps them prepare for different types of exam questions.
9. How can Vedantu’s important questions guide students in their study sessions?
Important questions provide a roadmap for study sessions, helping students focus on what is most important. This targeted approach makes studying more efficient and effective.
10. What is the benefit of discussing important questions with peers at Vedantu?
Discussing important questions with classmates allows students to share insights and clarify doubts. Collaborative learning can deepen understanding and enhance retention of information.
11. How can teachers use Vedantu’s important questions to support students?
Teachers can use important questions to assess student understanding and identify topics that need further clarification. This helps ensure that students are well-prepared for exams.
12. What resources are available on Vedantu related to important questions for this chapter?
On the Vedantu website, students can find important questions, NCERT solutions, and study materials specifically for Class 8 Science Chapter 4, which can aid their preparation.
13. How do important questions help students relate concepts to real-life situations?
Important questions often include scenarios that relate combustion and flame to everyday life. This connection helps students understand the practical applications of what they learn.
14. Why is it important for students to engage with important questions regularly?
Regular engagement with important questions helps reinforce learning and keeps information fresh in students' minds. This consistent practice is key to performing well in exams.
