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Combustion and Flame

In hydrocarbon fire extinguishers, CO₂comes out in the form of

a) Vapour.
b) Foam.
c) Spray.
d) Droplets.

✔Answer

✔Solution

Correct Answer Is : Foam.

Solution Is : For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide is the best extinguisher. Carbon dioxide being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.

The zone of no combustion is

a) The middle zone
b) Outermost zone
c) The base of the flame
d) Innermost zone.

✔Answer

✔Solution

Correct Answer Is : Innermost zone.

Solution Is : Here the wax vapours are unburnt as they do not get O₂.

Example of rapid combustion is

a) Human body metabolism.
b) Burning of LPG.
c) Burning of crackers.
d) Reaction of sodium with O₂.

✔Answer

✔Solution

Correct Answer Is : Burning of LPG.

Solution Is : It readily catches fire.

The substance which burns when reacts with O₂ is called

a) Burning substance.
b) Inflammable substances.
c) Non-combustible substances.
d) Combustible substances.

✔Answer

✔Solution

Correct Answer Is : Combustible substances.

Solution Is : They burn when come in contact with fire.

The white marble of Taj Mahal is changed to yellow because of

a) Global warming.
b) Deforestation.
c) Fog.
d) Acid rain.

✔Answer

✔Solution

Correct Answer Is : Acid rain.

Solution Is : When rain water dissolves oxides of sulphur and nitrogen produced due to burning of fossil fuels in the atmosphere, rain water is containimated with acids. Such rain is known as acid rain. Acid rain damages crops, buildings and statues.

Unburnt carbon particles in a fuel may cause

a) Typhoid.
b) Cholera.
c) Asthma.
d) Malaria.

✔Answer

✔Solution

Correct Answer Is : Asthma.

Solution Is : Unburnt carbon particles are produced by burning of carbon fuels like coal, wood etc. These are dangerous pollutants in air causing respiratory diseases. For example, asthma, bronchitis etc.

An example of a fuel is

a) Food.
b) Glass.
c) Stone.
d) Water.

✔Answer

✔Solution

Correct Answer Is : Food.

Solution Is : Food is a fuel in our body as it is broken down by reaction with oxygen to give energy.

Water is used to extinguish fires involving

a) Oil.
b) Wood or paper.
c) Electrical equipments.
d) Petrol.

✔Answer

✔Solution

Correct Answer Is : Wood or paper.

Solution Is : Water is the most common fire extinguisher. It is suitable when fires involve wood or paper. It is not suitable when electrical equipment is on fire because it may conduct electricity and harm those trying to extinguish the fire. It also cannot work for fires involving oil and petrol because it is heavier than oil.

The efficient fuel is

a) Coal.
b) Kerosene.
c) Wood.
d) LPG.

✔Answer

✔Solution

Correct Answer Is : LPG.

Solution Is : LPG is Liquefied Petroleum Gas. It is more efficient than coal, wood or kerosene because of its high calorific value (55000 kJ/kg) and comparatively easier to transport.

An example of inflammable substance is

a) Paper.
b) Straw.
c) Alcohol.
d) Wood.

✔Answer

✔Solution

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Class 8 Science Study Material

Combustion and Flame

In hydrocarbon fire extinguishers, CO2comes out in the form of

Correct Answer Is : Foam.

Solution Is : For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide is the best extinguisher. Carbon dioxide being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.

The zone of no combustion is

Correct Answer Is : Innermost zone.

Solution Is : Here the wax vapours are unburnt as they do not get O2.

Example of rapid combustion is

Correct Answer Is : Burning of LPG.

Solution Is : It readily catches fire.

The substance which burns when reacts with O2 is called

Correct Answer Is : Combustible substances.

Solution Is : They burn when come in contact with fire.

The white marble of Taj Mahal is changed to yellow because of

Correct Answer Is : Acid rain.

Solution Is : When rain water dissolves oxides of sulphur and nitrogen produced due to burning of fossil fuels in the atmosphere, rain water is containimated with acids. Such rain is known as acid rain. Acid rain damages crops, buildings and statues.

Unburnt carbon particles in a fuel may cause

Correct Answer Is : Asthma.

Solution Is : Unburnt carbon particles are produced by burning of carbon fuels like coal, wood etc. These are dangerous pollutants in air causing respiratory diseases. For example, asthma, bronchitis etc.

An example of a fuel is

Correct Answer Is : Food.

Solution Is : Food is a fuel in our body as it is broken down by reaction with oxygen to give energy.

Water is used to extinguish fires involving

Correct Answer Is : Wood or paper.

The efficient fuel is

Correct Answer Is : LPG.

Solution Is : LPG is Liquefied Petroleum Gas. It is more efficient than coal, wood or kerosene because of its high calorific value (55000 kJ/kg) and comparatively easier to transport.

An example of inflammable substance is

Correct Answer Is : Alcohol.

Solution Is : Inflammable substances have very low ignition temperature and can easily catch fire with a flame. For example, alcohol, petrol etc.

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In hydrocarbon fire extinguishers, CO₂comes out in the form of

Solution Is : Here the wax vapours are unburnt as they do not get O₂.

The substance which burns when reacts with O₂ is called