# Ncert Exemplar Solutions Class 8 Science Combustion and Flame

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## Ncert Exemplar Solutions Class 8 Science Combustion and Flame

Welcome to NCTB Solutions. Here with this post we are going to help 8th class students for the Solutions of NCERT Exemplar Class 8 Science Book, Unit 6, Combustion and Flame. Here students can easily find step by step solutions of all the problems for Combustion and Flame, Also here our Science teacher’s are solved all the questions with easily understandable language with proper guidance so that all the students can understand easily.

Combustion and Flame all Question Solutions :

Multiple Choice Questions :

Question no – (1)

A substance which reacts with oxygen giving heat is called a combustible substance. Which, one of the following is a combustible substance?

Correct option – (d)

Wood is a combustible substance.

Question no – (2)

Which one of the following has the highest calorific value?

Correct option – (c)

LPG has the highest calorific value.

Question no – (3)

Magnesium ribbon on burning in air produces

Correct option – (c)

Magnesium ribbon on burning in air produces magnesium oxide, heat and light.

Question no – (4)

Which of the following is not a combustible substance?

Correct option – (b)

Glass is not a combustible substance.

Question no – (5)

The substance that does not burn with flame is

Correct option – (d)

The substance that does not burn with flame is charcoal.

Question no – (6)

On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of non-availability of

Correct option – (a)

This is because of non-availability of Oxygen.

Question no – (7)

If a person’s clothes catches fire, the best way to extinguish the fire is to:

Correct option – (c)

The best way to extinguish the fire is to cover the person with a woolen blanket.

Question no – (8)

The substance expected to have the highest ignition temperature out of the following is

Correct option – (c)

The substance have the highest ignition temperature is Coal.

Question no – (9)

Choose the correct statement about inflammable substances from the following.

Correct option – (c)

Low ignition temperature and can catch fire easily.

Question no – (10)

Choose the incorrect statement from the following

Forest fires are usually due to:

Correct option – (c)

Cutting of trees – This is the incorrect statement.

Question no – (11)

The calorific value of a fuel is expressed in a unit called

Correct option – (d)

The calorific value of a fuel is expressed in a unit called Kilojoule per kilogram.

Question no – (12)

In villages, people use wood as fuel because:

Correct option – (b)

In villages, people use wood as fuel because of its easy availability and low cost.

Question no – (13)

Which among the following is considered as the cleanest fuel?

Correct option – (d)

Hydrogen gas is considered as the cleanest fuel.

Question no – (14)

Choose the incorrect statement from the following. A good fuel is one which :

Correct option – (c)

A good fuel is one which leaves behind many undesirable substances.

Question no – (15)

Shyam was cooking potato curry on a chulha. To his surprise he observed that the copper vessel was getting blackened from outside. It may be due to :

Correct option – (c)

To his surprise he observed that the copper vessel was getting blackened from outside. It may be due to improper combustion of the fuel.

Very Short Answer Questions :

Question no – (16)

(a)Chemical process in which a substance reacts with oxygen to give off heat is called combustion.

(b) When the clothes of a person catch Fire, the person is covered with a Blanket to extinguish fire.

(c) The Lowest temperature at which a substance catches fire is called its Ignition temperature.

(d) The substances which have very Low ignition temperature and can easily catch fire with a flame are called Inflammable substances.

(e) The substances which vapourise during Burning, give flame.

Question no – (17)

(a) Diesel is a combustible substance

(b) Glass is a non-combustible material

(c) Matchstick does not burn by itself.

(d) Some substances on combustion produce Heat and Flame.

(e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its Calorific value.

Question no – (18)

In glass B the candle will remain lighted for a longer duration because it contains oxygen which is a supporter of combustion while glass A contains carbon dioxide which prevents combustion.

Question no – (19)

In order to boil the water faster Anu should place the test tube in the outer zone of the flame because this zone are usually the hottest part of a flame.

Question no – (20)

The use of fuels like petrol and diesel releases toxic gases into the atmosphere, which plays a significant role in the downgrade of air quality level. So replacing petrol and diesel with CNG which is a natural gas will have no effect at all on the air quality level of an area.

Short Answer Questions :

Question no – (21)

Combustible material : – Straw, Charcoal, Cardboard, Paper, Candle wood.

Non-Combustible material : – Chalk , Stone, Iron road, Copper coin, Glass.

Question no – (22)

(a) Air is necessary for combustion

This statement is True.

(b) Magnesium is a non-combustible metal

This statement is False.

Reason : Magnesium is a combustible material

(c) Carbon dioxide is an excellent fire extinguisher

This statement is True.

(d) Calorific value of wood is higher than that of coal

This statement is False.

Reason : Calorific value of coal is higher than that of wood.

Question no – (23)

(a) Oxides of sulphur and nitrogen → (iv) acid rain.

(b) CNG → (vi) fuel for automobiles.

(c) Oxygen → (v) necessary for combustion.

(d) Inflammable substance → (iii) very low ignition temperature.

(e) Carbon dioxide → (i) fire extinguisher.

(f) Carbon monoxide → (ii) incomplete combustion of coal.

Question no – (24)

(a) Hottest part → outer zone of complete combustion → Blue.

(b) Moderately hot → middle zone of partial combustion → Yellow.

(c) Least hot → innermost zone of unburnt wax vapours → Black.

Question no – (25)

If we hold a piece of iron wire inside a candle flame of Bunsen burner flame we will notice that the iron being a non combustible and non vaporizing material has became red and hot but it is not producing a flame.

Question no – (26)

(a) A chemical process in which a substance reacts with oxygen to give off heat is called Combustion.

(b) Wood, paper, CNG are Combustible substances.

(c) The lowest temperature at which a substance catches fire is called its Ignition temperature.

(d) Ignition temperature of Petrol is lower than that of wood.

(e) The substances which have very low Ignition temperature and can easily catch fire with a flame are called Inflammable substances.

(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its Calorific value.

Question no – (27)

People should keep their doors and windows open while burning an Angethi. The burning of Angethi releases toxic gases which will fill up the room if the doors and windows are kept closed. Due to lack of oxygen the people in the room will face difficulty in breathing and might even die.

Question no – (28)

(a) A physical process in which a substance reacts with oxygen to give off heat is called combustion.

This statement is False.

Reason : A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

(b) Water is the best extinguisher for fires involving electrical equipment.

This statement is False.

Reason : Carbon dioxide is the best extinguisher for fires involving electrical equipment.

(c) Alcohol, CNG and LPG are inflammable substances.

This statement is True.

(d) Increased concentration of nitrogen in air is believed to cause global warming.

This statement is False.

Reason : Increased concentration of Carbon dioxide in air is believed to cause global warming

(e) Greater the calorific value, better is the fuel.

This statement is True.

(f) Middle zone is the hottest zone of a flame.

This statement is False.

Reason : The outer zone is the hottest zone of a flame.

(g) The substances which vapourise during burning, give flame.

This statement is True.

Question no – (29)

When a cracker is ignited a chemical reaction takes place which releases a large amount of gas with immense pressure, this results in the creation of an explosion like sounds along with some lights and heat.

Question no – (30)

Fuel efficiency is the amount of heat energy that is produced when 1 kg of that fuel is burnt completely. The more heat energy produced the more is the efficiency of that particular fuel. It is often referred to as as the calorific value of that fuel.

Long Answer Questions :

Question no – (31)

Out of the three watch glasses the glass containing petrol will catch fire instantly. Petrol have very low ignition temperature that is it is an inflammable substances due to this property it catches fire far more easily. On the other hand milk and mustard oil have high ignition point so they don’t catch with that much ease.

Question no – (32)

No, Manu’s actions were not suitable for the moment. Oils are lighter than water so when someone tries to extinguish flames on oil with water, the flame will get more aggressive as the flame will now float on the water. She should have tried to keep a lid on her pan which will prevent the oxygen from coming in contact with the flame, this action would have extinguished the flame.

Question no – (33)

The three essential requirements to produce fire are :

• Fuel – The substance that undergoes combustion is said to be a fuel.

• Oxygen – Oxygen supports combustion of a fuel.

• Heat – Heat is necessary to increase the temperature of the fuel to its ignition temperature.

A fire extinguisher is often used in places where an electrical appliances or an inflammable substances is burning. It prevents short circuit in electrical appliances and does not have hampers the functioning of the appliances. It acts as a blanket preventing oxygen to come in contact with the fuels, so it is great for extinguishing fires on fuels like oils.

Question no – (34)

The two examples each for a solid, liquid and gaseous fuel are :

• Solid fuels : Coals and wood . Wood are generally used in rural areas to cook food or for warming their body in cold climate. Coal are generally used for electricity production and in industrial processes.

• Liquid : Diesel and Petrol. Both of these fuels are generally used to power vehicles engine.

• Gaseous fuels : CNG and LPG. LPG are used to fill household cylinder that are used to cook food whereas CNG are used to vehicles such as buses and car.

Question no – (35)

I would choose the car which will run on CNG because CNG is nearly close to Petrol in terms of calorific value or efficiency but it exceeds in reducing carbon emissions in the atmosphere or in simpler words it is more environmental friendly.

Question no – (36)

Wood has a very high calorific value and it is great furl. But we should try to limit the use of wood as a fuel because it combustion produces a lot of smoke in the environment which are responsible for air pollution and moreover the cutting of wood for fuel will to be too devastating for nature to maintain balance in earth.

Question no – (37)