Class 8 chemistry MCQs with answers are provided here for chapter 6, combustion and flame. These MCQs are based on the CBSE board curriculum and correspond to the most recent Class 8 chemistry syllabus. By practising these Class 8 multiple choice questions, students will be able to quickly review all of the ideas covered in the chapter and prepare for the Class 8 annual examinations as well as other competitive exams.
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Class 8 Combustion and Flame MCQs
Q-1: Which of the following is a chemical reaction that produces heat when a substance reacts with oxygen?
a) Oxidation
b) Combustion
c) Reduction
d) Hydrolysis
Answer: b) Combustion
Explanation: Combustion is a chemical reaction in which a substance reacts with oxygen to produce heat.
Q-2: Ignition temperature is the ________ temperature at which the substance catches fire.
a) Highest
b) Lowest
c) Maximum
d) Room
Answer: b) Lowest
Explanation: The lowest temperature at which a substance catches fire is referred to as its ignition temperature.
Q-3: A mixture of antimony trisulphide, potassium chlorate, and white phosphorus, along with glue and starch, was applied to the head of a suitable wood match. Which of the following chemicals ignites when struck against a rough surface?
a) Antimony trisulphide
b) White Phosphorous
c) Glue
d) Starch
Answer: b) White Phosphorous
Explanation: The heat of friction caused white phosphorus to ignite when it was struck against a rough surface. As a result, the match began to burn.
Q-4: Which of the following is not an inflammable substance?
a) Alcohol
b) Wood
c) Ethanol
d) Liquified Petroleum Gas
Answer: b) Wood
Explanation: Inflammable substances are those that have a very low ignition temperature and can easily catch fire with a flame. Inflammable substances include gasoline, alcohol, and liquefied petroleum gas (LPG). Hence, only wood is an inflammable substance.
Q-5: Which of the following is the best fire extinguisher for electrical equipment and inflammable substances?
a) Water
b) CO2
c) O2
d) All of the above
Answer: b) CO2
Explanation: Carbon dioxide (CO2) is the best extinguisher for fires involving electrical equipment and inflammable materials such as gasoline. Because CO2 is heavier than oxygen, it blankets the fire. The fire is under control because the contact between the fuel and the oxygen has been cut off. CO2 has the added benefit of not causing damage to electrical equipment in most cases.
Q-6: Which of the following describes a type of combustion in which a substance suddenly bursts into flame without any apparent cause?
a) Rapid
b) Explosion
c) Spontaneous
d) None of the above
Answer: c) Spontaneous
Explanation: The type of combustion in which a material spontaneously bursts into flames without any apparent cause is known as spontaneous combustion.
All other types of combustion, on the other hand, require the application of heat in order to ignite.
Q-7: Which of the following is not an ideal fuel characteristic?
a) Costly
b) Readily available
c) Easy to transport
d) High calorific value
Answer: a) Costly
Explanation: An ideal fuel is inexpensive, widely available, easily combustible, and portable. It has a high calorific value. It emits no gases or residues that pollute the environment.
Q-8: Which of the following units expresses fuel efficiency in terms of calorific value?
a) kg/kJ
b) kJ/kg
c) J/kg
d) J/g
Answer: b) kJ/kg
Explanation: Fuel efficiency is measured in terms of calorific value, which is measured in kilojoules per kilogramme (kJ/kg).
Q-9: Which of the following does not burn with a flame?
a) Molten wax
b) Kerosene oil
c) Charcoal
d) Camphor
Answer: c) Charcoal
Explanation: The substances that vaporise during combustion produce flames. For example, kerosene oil and molten wax rise through the wick and are vapourised during burning and form flames. Charcoal, on the other hand, does not. As a result, no flame is produced.
Q-10: Which of the following is a fuel that is good for the environment and is used in automobiles?
a) Diesel
b) Petrol
c) Natural gas
d) Petroleum gas
Answer:c) Natural gas
Explanation: When carbon-containing fuels such as wood, coal, and petroleum are burned, they produce air pollution, respiratory problems, acid rain, and global warming. However, CNG (Compressed Natural Gas) is referred to as a cleaner fuel because it emits very little harmful gas.
Q-11: Which of the following fuels has a calorific value of 45000 kJ/kg?
a) Cow dung cake
b) Petrol
c) LPG
d) Biogas
Answer: b) Petrol
Explanation: Below table shows the calorific value for various different fuels:
| Fuel | Calorific Fuel ( kJ/kg) |
|---|---|
| Cow dung cake | 6000-8000 |
| Petrol | 45000 |
| LPG | 55000 |
| Biogas | 35000-40000 |
The table clearly shows that petrol has a calorific value of 45000 kJ/kg.
Q-12: It is dangerous to burn wood in a room. The gas X produced can be fatal to the person sleeping in the room. Identify the gas X.
a) CO2
b) SO2
c) CO
d) N2
Answer: c) CO
Explanation: It is dangerous to burn wood in a room because wood burns incompletely and emits CO gas. The CO gas produced is lethal to anyone sleeping in the room.
Q-13: Which type of combustion is exemplified by the combustion of match sticks?
a) Explosive combustion
b) Spontaneous combustion
c) Rapid combustion
d) None of the above
Answer: c) Rapid combustion
Q-14: Which zone of the candle flame burns with a blue flame?
a) Outer zone
b) Middle zone
c) Innermost zone
d) All of the above
Answer: a) Outer zone
Explanation: A candle flame’s outer zone is a zone of complete combustion that burns with a blue flame. It’s also the hottest area.
Q-15: Which type of fire can be safely extinguished with water?
a) Fire caused by petrol
b) Fire caused by oil
c) Fire caused by electrical equipment
d) Fire caused by wood
Answer: d) Fire caused by wood
Explanation: Water only works when materials such as wood and paper are on fire. Water may conduct electricity and harm those attempting to extinguish a fire if electrical equipment is on fire. Water is incompatible with fires involving oil and gasoline because it is heavier than oil and gasoline.
Q-16: Which of the following substances has the lowest ignition temperature?
a) Charcoal
b) Paper
c) Wood
d) White Phosphorus
Answer: d) White Phosphorus
Explanation: Substances with a lower ignition temperature easily catch fire. White phosphorus has the lowest temperature of all, with a temperature of around 30oC.
Q-17: Which of the following candle flame zones is characterised by the deposition of unburned carbon particles?
a) Luminous zone
b) Non luminous zone
c) Middle zone
d) Outer zone
Answer: a) Luminous zone
Explanation: The deposition of unburnt carbon particles is present in the luminous zone of the flame.
Q-18: Which of the following gases is produced when there is sufficient oxygen supply?
a) CO
b) CO2
c) Both CO and CO2
d) N2
Answer: b) CO2
Explanation: Complete combustion occurs in the presence of sufficient oxygen, resulting in the release of carbon dioxide gas.
Q-19: Which of the following is not a combustible substance?
a) Iron Rod
b) Wood
c) CNG
d) Paper
Answer: a) Iron Rod
Explanation: Combustible substances are those that can be easily burned, whereas non-combustible substances are those that cannot be easily burned. Wood, CNG, and paper are combustible materials, whereas iron rod is not.
Q-20: Which of the following are necessary requirements for producing a fire?
a) Fuel, N2, Heat
b) CO2, Water, O2 gas
c) Fuel, O2, Water
d) Fuel, O2, Heat
Answer: d) Fuel, O2, Heat
Explanation: Fuel, air (to supply oxygen), and heat (to raise the temperature) are all required for the production of fire.
Read Also:
- Combustion and Flame
- Combustion and Its Types
- Introduction to Candle Flame
- Chapter 6-Combustion and Flame Worksheet Set 1
- Chapter 6-Combustion and Flame Worksheet Set 2
- Chapter 6-Combustion and Flame Worksheet Set 3
- Chapter 6-Combustion and Flame Important Questions with Answers
- Chemistry Concept Questions and Answers
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