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CBSE Questions for Class 8 Chemistry Combustion And Flame Quiz 6 - MCQExams.com
CBSE
Class 8 Chemistry
Combustion And Flame
Quiz 6
How individuals can help to prevent acid rains?
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By using public transportation
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Using the electrical energy efficiently
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Simply walking wherever possible
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All
Explanation
All the above activities result in the less use of fossil fuels, and hence less release of acid rain causing oxides.
Hence the correct option is D.
What is the factor that differentiates between combustion and burning?
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Amount of oxygen used
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Environment
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Material
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None of the above
Explanation
They are different with respect to the combustion is done in a fixed amount of oxygen while in burning it has the access of infinite amount of oxygen (done in open).
Hence option (A) is correct.
Hence, the correct option is $$A$$
Combustion of most fuels releases:
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$$CO_2$$
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$$SO_2$$
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$$NO_2$$
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$$O_2$$
Explanation
Fuels are mainly composed of carbon. Fuel burn when they react with oxygen which is present in air to form carbon dioxide.
$$C + O_2 \rightarrow CO_2$$
What happens to ignition temperature of a substance as the pressure of oxygen concentration decreases?
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It decreases
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It increases
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No change
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None of the above
Explanation
As the supply of oxygen decreases the substance does not get the required energy to undergo combustion. It is same as the activity of paper cup where the cup having water doesn't burn easily because the ignition temperature has not met. So here also if the pressure of the oxygen concentration decreases its ignition temperature will increase.
Option $$B$$ is correct.
Which is the hottest part in the flame of the candle?
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Blue
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Yellow
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Black
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Wax part
Explanation
The hottest part of a candle flame are actually the blue, almost invisible area near the base. Where oxygen is drawn in and blue or white part around the edge. In this area flame meets the oxygen-rich air all around it.
The flame get progressively cooler as you move in from the outside edge toward the wick.
By undergoing what process, chemical fuel releases its energy?
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Reduction
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Oxidation
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Electrolysis
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decomposition
Explanation
Chemical fuels react with oxygen (combustion) and releases their energy.
Hydrocarbon combustion refers to the chemical reaction where a hydrocarbon reacts with oxygen to create carbon dioxide, water, and heat.
Why is CNG a cleaner fuel?
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No particulate emission
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Releases very less amounts of sulphur and nitrogen oxides
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No emission of ash
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All of the above
Explanation
C.N.G (compressed natural gas) is a cleaner fuel because it causes less pollution by emitting fewer pollutants like carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide, particulate matter, unburned hydrocarbons etc.
Rapid combustion is:
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when gas burns, it produces heat and light.
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when material suddenly burst into flames.
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when there is evolution of heat.
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none of these.
Explanation
Combustion in which a substance burns rapidly and produces heat and flame is known as rapid combustion. Example: combustion of LPG gas, petrol, etc. Substances which undergo rapid combustion have lower ignition temperature.
In combustion, the substance reacts with ___________.
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hydrogen
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oxygen
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nitrogen
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carbon dioxide
Explanation
Combustion is an exothermic reaction between fuel and oxidant usually atmospheric oxygen.
The hottest part of a candle flame is the __________.
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luminous zone
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dark zone
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hot zone
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non-luminous zone
Explanation
The Non-Luminous zone is the region of the complete combustion.
If you look at a candle flame closely. You will see an "aura" formed around the candle.
Since this zone is complete combustion and it is the hottest part of the flame.
It is difficult to burn a heap of green leaves because ____________.
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the green colour prevents them from burning
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of the thick material from which they are made
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the size of the heap is too large
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they contain a great amount of moisture which makes the ignition temperature high
Explanation
The heap of green leaves has a great amount of moisture content which makes the ignition temperature high. Hence it is difficult to burn green leaves.
So, the correct option is $$D$$
What is ignition temperature of a fuel?
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Very high temperature
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The
ignition temperature
of a fuel
is the lowest temperature at which the vapour of that
fuel
will continue to burn
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Very low temperature
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none of these
Explanation
The fire point of a fuel is the lowest temperature at which the vapor of that fuel will continue to burn for at least five seconds after ignition by an open flame of standard dimension.
Burning which of the following fuels causes relatively lesser damage to the environment in comparison to others?
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Diesel
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Petrol
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C.N.G
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Cow dung
Explanation
On combustion, C.N.G releases a very less amount of sulphur and nitrogen oxides, compared to all other fuels, without any particulate emission.
Non-combustible gas among the following is _______________.
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hydrogen
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oxygen
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L.P.G
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natural gas
Explanation
Oxygen is non-combustible gas. It only supports the process of combustion.
Ignition temperature of flammable substances is _____________.
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high
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low
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very high
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None
Explanation
Flammable substances are the one whose ignition temperature is low as they can easily catch fire.
Hence the option B is correct.
Which
among the following
is not flammable?
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Rubber
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Wood
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Methanol
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Water
Explanation
Water is not flammable as it has a high ignition point.
The reason that water (in any state) is not flammable is that it is already the product of combustion.
Which of the following is(are) characteristic(s) of a flammable substances?
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High ignition temperature
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Low ignition temperature
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High boiling point
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Both A and B
Explanation
The lowest temperature at which a
substance catches fire is called its
ignition temperature.
A flammable substance can easily catch fire as it has a low ignition temperature.
Hence option B is correct.
Which of the following parameters can be used to control fire?
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Cutting off the oxygen supply
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Suppressing the fuel supply
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Reducing the area over which the fire exists
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All of the above
Explanation
A substance burns only in the presence of oxygen. So, cutting off the oxygen supply can stop the fire. Also, if the fuel supply is suppressed, the fire can not continue burning at the same rate. Additionally, reducing the accidental area makes the combustion less violent.
So, option D is correct.
Which of the following has the lowest ignition temperature?
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Coal
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Wood
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Paper
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Kerosene
Explanation
Coal ignition temperature:
$$454^oC$$
Wood ignition temperature:- More than $$300^oC$$
Paper ignition temperature:
$$233^oC$$
Kerosene ignition temperature:
$$220^oC$$
Which of the following can undergo spontaneous combustion?
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Petrol
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Diesel
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Hay
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All of the above
Explanation
Hay can catch fire under normal conditions. Hence, it can undergo spontaneous combustion.
What do we need to get 100% fuel efficiency?
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Ideal fuel
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Ideal engine
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Ideal driver
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Both A and B
Explanation
To convert all the thermal energy into work we need an ideal engine and ideal fuel.
Thus we can get 100% fuel efficiency.
Both A and B are correct.
Hence, the correct option is $$D$$.
Which of the following do not produce flame on burning?
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Petrol
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Coal
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L.P.G
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Kerosene
Explanation
Coal burns directly without getting vaporised. So it does not produce the flame. It burns with a glow.
A
form of combustion reaction where there is a release of high amount of
heat and light energy in a small interval of time is _____________.
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spontaneous combustion
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rapid combustion
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fast combustion
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instant combustion
Explanation
Rapid Combustion is the process in which a substance burns rapidly and produces heat and light. Hence, a form of combustion reaction where there is a release of a high amount of heat and light energy in a small interval of time is '
Rapid Combustion
'.
Hence, the correct option is $$\text{B}$$
Which of these is necessary for combustion?
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Fuel
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Supply of oxygen
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Source of ignition
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All of the above
Explanation
We need fuel (combustible substance), oxygen (supporter of combustion) and a source of ignition to initiate the combustion.
Hence, the option D is correct.
The innermost zone of candle flame is the least hot due to the presence of :
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unburnt wax vapour.
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no supply of oxygen.
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presence of wick.
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all the above
Explanation
The innermost zone is the least hot and black in color. This is due to the presence of unburned wax vapors.
Hence, option A is correct.
Fuel efficiency depends on:
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properties of fuel
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amount of oxygen available
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Both A and B
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None of the above
Explanation
Fuel efficiency depends on the calorific value of the fuel. Also, the amount of oxygen available affects how well the fuel burns. Less amount of oxygen will result in incomplete combustion and thus, will cause low fuel efficiency.
Colour of the flame is dependent on the ______________.
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Supply of oxygen
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Nature of fuel
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Ignition temperature of the fuel
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All of the above
Explanation
The color and temperature of a flame are dependent on the nature of the fuel involved in the combustion.
When excited, every element can emit light at a specific wavelength, hence the color of the emitted light is characteristic of each element. An example of this is the blue flame from gas ovens, which is due to the combustion of methane or liquified petroleum gas.
Which of the following materials does not undergo rapid combustion?
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Wood
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Petrol
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Paper
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Matchstick
Explanation
Rapid combustion is the process in which a substance burns rapidly and produces heat and light. Petrol, paper and matchstick burn rapidly and so, undergo rapid combustion.
However, wood's ignition temperature is very high and so, it burns slowly.
Hence, the option A is correct.
Which of the following statement is not correct?
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Air is essential for the burning process
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The flame of a burning candle can be put off by placing a cover cap over the flame
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Burning of coal cannot be stopped by covering it with sand
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Burning of wood can be stopped by covering it with sand
Explanation
The burning of coal can be
stopped by covering it with sand.
When sand is thrown over burning kerosene oil, the sand covers it like a blanket. The sand cuts off the air supply to the burning kerosene oil due to which the fire gets extinguished.
The form of combustion where a material suddenly undergoes combustion under normal conditions is known as:
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fast combustion
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spontaneous combustion
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slow combustion
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non-spontaneous combustion
Explanation
A type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is known as spontaneous combustion.
For some materials, ignition temperature is lower than the room temperature and hence, they readily catch fire even at room temperatures. Phosphorus is an example of such a material.
Hence, the form of combustion where material undergoes combustion at room temperature that is under normal conditions is known as '
Spontaneous Combustion
'.
Hence, option B is correct.
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