Test: Combustion & Flame- 1 - Class 8 MCQ

To explain why "B: Fuel" is the correct answer:

- Fuel:
- Fuels are substances that can undergo combustion to release heat and light.
- During combustion, chemical energy stored in the fuel is converted into heat and light energy.
- This process is essential for generating energy in various forms, like in engines, stoves, or power plants.
- Examples of fuels include wood, coal, oil, gas, and gasoline.

Therefore, fuel is the substance that gives heat and light after combustion.

• The calorific value measures the energy produced by a fuel when consumed.
• It is expressed in kilojoules per kilogram (kJ/kg), indicating how much energy is released from one kilogram of fuel.
• This unit helps compare the efficiency of different fuels based on their energy content.
• Other options like kilogram per kilojoule or kilogram per litre do not represent energy output effectively.

Air is needed for fire to burn. By cutting off the supply of air, you can control or put out a fire. This stops the fire from getting the oxygen it needs to keep burning.

LPG is a better domestic fuel as it burns cleanly without producing smoke or unburnt carbon particles, which can cause respiratory problems.

The statement "The flame of a candle is non-luminous" is false because a candle flame is luminous, meaning it emits visible light. The yellowish part of a candle flame comes from the glowing carbon particles produced during the incomplete combustion of the wax, making the flame visible to the human eye.

The amount of heat energy released on complete combustion of 1 kg of fuel is called calorific value of that fuel. Higher the calorific value better the fuel is considered.

The lowest temperature at which substance catch fire is called ignition temperature. The fuel with moderate temperature is considered better fuel for domestic use.

Carbon dioxide gas is used in fire extinguisher to cut the oxygen supply.
Option A is correct.

Aluminium absorbs heat, lowering the temperature of the paper wrapped around it and preventing it from reaching its ignition temperature, so it does not catch fire easily.

The three essential requirements for producing fire are fuel, air (to supply oxygen), and heat (to raise the temperature of the fuel beyond the ignition temperature). Fire can be controlled by removing one or more of these requirements.