CBSE Questions for Class 8 Chemistry Combustion And Flame Quiz 3 - MCQExams.com

Unburnt carbon particles are present in the:
  • Blue zone
  • Dark inner zone
  • Luminous zone
  • Non-luminous zone
What kind of combustion is undergone by ignition of a cracker?
  • Explosive combustion
  • Spontaneous combustion
  • Rapid combustion
  • Slow combustion
Which among the following is considered as the cleanest fuel?
  • Cow dung cake
  • Petrol
  • Kerosene
  • Hydrogen gas
Coke is a _______ fuel.
  • harmless
  • renewable
  • smokeless
  • None of these
Choose the correct statement from the following.
A good fuel is one which:
  • is readily available
  • produces a large amount of heat
  • leaves behind many undesirable substances
  • burns easily in air at a moderate rate
Autoignition temperature is the highest temperature at which a substance can burn.
  • True
  • False
Air is necessary for burning as it supplies oxygen which is essential for combustion.
  • True
  • False
Which of the following is not required for combustion to take place?
  • Fuel
  • Carbon dioxide
  • Oxygen
  • Source of heat
It is difficult to burn a heap of green leaves but dry leaves catch fire easily.
  • True
  • False
The products formed when a candle burns in air are:
  • nitrogen
  • carbon monoxide
  • carbon dioxide
  • carbon in the form of soot
Burning is a rapid oxidation process in which heat and light are evolved.
  • True
  • False
During combustion of gaseous fuels, deficiency of air ___________.
  • Lengthens the flame.
  • Tends to shorten the flame.
  • Does not affect the flame length.
  • Increases the flame temperature.
Higher efficiency in the combustion of solid fuel cannot be achieved by __________.
  • Supplying correct quantity of combustion air
  • Keeping the flue gas exhaust temperature very high
  • Proper fuel preparation
  • Adopting efficient fuel firing techniques and equipments
A substance which burn in air is  __________ (combustible/ non-combustible) substance such as ____________ (hydrogen/ ammonia/ chlorine).
  • Non-combustible, chlorine
  • Combustible, hydrogen
  • Combustible, ammonia
  • Combustible, chlorine
Which of the following property is not a characteristic of a good fuel?
  • High ignition temperature
  • Low cost
  • Causes minimum pollution
  • Readily available
Stack heat losses can be minimized by ____________.
  • controlling the excess air.
  • oxygen enrichment of combustion air.
  • using low c.v. fuels.
  • maintaining proper draft in the furnace.
The products of a burning candle are:
  • ash and water vapour
  • $$CO_2$$ and water vapour
  • wax and water vapour
  • only melted wax
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that __________.
  • the food is not cooked completely
  • the fuel is not burning completely
  • the fuel is wet
  • All of above
A thin paper cup filled with water does not catch fire when placed over a flame. This is because:
  •  water cuts off oxygen supply to the paper cup
  • water is an excellent conductor of heat
  • the paper cup does not become appreciably hotter than the water it contains
  • paper is a poor conductor of heat
 $$CO_2$$ is able to control fires by disconnecting the supply of oxygen.
  • True
  • False

The different zones of a candle flame are marked by the letters, A, B and C. Which of the following is correct?
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  • B is the hottest part of the flame.
  • C is moderately hot.
  • A is the hottest part of the flame.
  • A is moderately hot whereas C is the coldest part.
Select the correct option that applies to gaseous fuels:
(A) have high ignition temperature
(B) have low calorific value
(C) are easy to ignite
(D) have high calorific value
  • A and B
  • B and C
  • C and D
  • D and B
The necessary conditions for the combustion process to occur are:
(A) availability of air/oxygen
(B) availability of air/oxygen and fuel
(C) the temperature of the fuel below the ignition temperature
(D) the temperature of fuel above the ignition temperature
Select the correct alternatives.
  • A and B
  • B and D
  • C and A
  • D and A
The essential requirements for producing a fire ___________.
  • fuel
  • air
  • heat
  • all of the above
Charcoal burn to produce heat, light and:
  • $$CO_2$$ 
  • $$O_2$$
  • $$H_2 $$
  • Both B and c
Which of the following is combustible?
  • Oxygen
  • Carbon dioxide
  • Hydrogen
  • All of these
Nitrogen ______.
  • supports combustion
  • does not support combustion
  • is non-flammable
  • is flammable
When sand is poured over some burning material, the fire goes off. It is because:
  • the ignition temperature is brought down by sand
  • supply of air is cut off
  • sand spreads easily
  • all of the above
The rubbing surface of a matchbox has which of the following element
  • Sodum
  • Potassium
  • Phosphorous
  • Carbon
Fuels can exist in which of the following states?
  • Solids
  • Liquids
  • Gases
  • All of these
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