# NCERT Solutions for Class 6 Science Chapter 15 Air Around Us

These NCERT Solutions for Class 6 Science Chapter 15 Air Around Us Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

## Air Around Us NCERT Solutions for Class 6 Science Chapter 15

### Class 6 Science Chapter 15 Air Around Us Textbook Exercise Questions and Answers

Question 1.
What is the composition of air?
Air is mixture of nitrogen, oxygen, carbon dioxide, water vapour and a few other gases. Some dust particles may also be present in it. Air is a mixture of gases, mainly containing nitrogen (about 78% by volume) and oxygen (about 21% by volume). The remaining 1% is made up gases, such as argon (about 0.9%), carbon dioxide (0.03%) and small amounts of other gases. Varying quantities of dust, smoke and water vapour are also present. The amount of these in the air varies from place to place and from time to time.

Question 2.
Which gas in the atmosphere is essential for respiration?
Oxygen gas in the atmosphere is essential for respiration.

Question 3.
How will you show that air supports burning?
Fix two burning candles of same size in the middle of two troughs. Fill the troughs with equal amounts of water. The water level should be below the height of candles. Light the candles and cover one of them with a bigger jar and the other one with a smaller jar. Observe carefully what happens to the burning candles and the water level. Note the time after which both the candles go off. You will observe that the candle covered with smaller glass jar extinguishes first and then the one covered with the bigger jar. Water level rises up in both the jars. This shows that air is required for buming/combustion. Bigger glass jar had more air inside it, so the candle kept burning for a longer time. Oxygen in the jar is consumed due to burning. Hence, water level rises up to fill the empty space in the jar.

Question 4.
How will you show that air is dissolved in water?
Take some water in a glass vessel or beaker. Heat it slowly on a tripod stand. Before the water begins to boil, look carefully at the inner surface of the vessel. You will see tiny bubbles on the inside. On heating, air dissolved in water escapes in the form of these bubbles. This shows that air is dissolved in water.

Question 5.
Why does a lump of cotton wool shrink in water?
Cotton lump contains air in it. There are various spaces in which air is filled. When cotton lump is put into water, air present in the vacant space dissolves in water and cotton lump shrinks.

Question 6.
The layer of air around the earth is known as ……………
Atmosphere.

Question 7.
The component of air used by green plants to make their food is …………….
Carbon dioxide.

Question 8.
List five activities that are possible due to presence of air.
The activities that are possible due to the presence of air are:

1. Rotation of windmills
2. Movement of sailing yachts
3. Flying of aeroplane, birds, etc.
4. Dispersal of seeds
5. Water cycle

Question 9.
How do plants and animals help each other in exchange of gases in the atmosphere?
Animals and plants use oxygen from air during respiration and release carbon dioxide gas in air. But green plants release oxygen gas by using carbon dioxide during photosynthesis. Thus, we can say that animals and plants help each other in exchange of gases.

NCERT Extended Learning Activities And Projects

Question 1.
On a clear glass window facing towards an open area, fix a small rectangular strip of paper. Remove the strip after a few days. Do you notice a difference between the rectangular section that was left covered with paper and the rest of the glass window? By repeating this exercise every month, you can have an idea about the amount of dust present in air around you at different times of the year.
Hint:
Do it yourself.

Question 2.
Observe the leaves of trees, shrubs or bushes planted by the roadside. Note whether their leaves have some dust or soot deposited over them. Take similar observations with the leaves of trees in the school compound or in a garden. Is there any difference in deposition of soot on leaves of trees near the roadside? What could be the possible reasons for this difference? Take a map of your city or town and try to identify regions in the map where you have noticed very thick layer of soot on the plants by the roadside. Compare with results obtained by other classmates and mark these areas on the map. Perhaps the results from all the students could be summarised and reported in newspapers.
Hint:
Do it yourself.

Activity 1

Objective: To show the presence of air.
Materials required: Wind vane mounted on a stick.
Procedure

• Take a firki mounted on a stick.
• Hold it by its stick and move it in different directions in an open area.

Observation: The firki starts rotating.
Conclusion: The firki moves when the air strikes its blades. This shows that air is present around us.

• We all breathe in air. Breathing is an essential part of respiration. We breathe in oxygen rich air and breathe out carbon dioxide rich air.
• Components of Air: Air contains mostly nitrogen and oxygen. Nitrogen occupies 78% of the air. Oxygen occupies 21% of the air. 1% of the air is made up of carbon dioxide, other gases, water vapour, dust particles, etc.

i. Nitrogen

• It is the lightest, colourless, odourless gas. It is used to control combustion.
• It is used by plants and animals to synthesise proteins in the body.
• It cannot be directly used by plants or animals. It has to be fixed into its nitrate or nitrite forms. This is done by bacteria living in root nodules of legumes.
• It is used to manufacture fertilisers to increase soil fertility.
• It is used to manufacture ammonia used in many industries.
• Nitrogen prevents oxidation of stored food in packets.

ii. Oxygen

• It is a chemical element in the form of gas. Mostly it is diatomic, made up of two atoms. O2 is the molecular oxygen.
• It is taken directly from the air by organisms living on land.
• It helps in oxidising the food eaten by organisms to release energy.
• Aquatic organisms take in oxygen dissolved in water.
• Oxygen is required for combustion.
• Oxygen in the form of ozone helps in the protection of living organisms from dangerous UV rays coming out from the sun.
• It is used as a fuel in rockets.
• It is stored in the cylinders and is used to artificial respiration to patients in the hospitals.

iii. Carbon dioxide

• It is the gas which is made up of one carbon atom combining with two atoms of oxygen (CO2).
• It is used by plants in synthesising their food by the process of photosynthesis.
• It is used in fire extinguishers.
• It is used in storing soft drinks.

iv. Inert gases

• These are also called as noble gases. They occupy a negligible percentage in air.
• Argon is used to fill the bulbs to prevent their filament.
• Helium is used in providing low temperatures.
• Neon is used to fill special bulbs called as neon signs.
• Radon is used in treating cancer patients.

v. Water vapour

• It is a gaseous form of water present as gas in the air.
• Amount of water vapour in the air varies with sun’s heat.
• Hot sun can evaporate more amount of water and convert it into water vapour.
• It helps in the formation of clouds which later can come down as rain.

vi. Dust and smoke

• Air contains some amount of dust and smoke in it.
• Dust and smoke are contributed by vehicles and industries releasing them.
• These are harmful to human beings and can cause many respiratory diseases.

Activity 2

Objective: To show the presence of dust particles in air.
Materials Required: Black chart papers and black curtain.
Procedure:

• Close all the doors and windows with curtains pulled down to make the room dark.
• Now, open the door or a window facing the sun, just a little, in such a way that it allows sunlight to enter the room only through a slit.
• Look carefully at the incoming beam of sunlight.

Observation: We see a large number of tiny- shining particles moving in the beam of sunlight. These are the dust particles
Conclusion: Air contains dust particles.

Oxygen-Carbon dioxide Levels:
Oxygen and carbon dioxide levels in the air are maintained by different processes like respiration and photosynthesis.

Respiration involves utilisation of oxygen from air by living organisms and releasing carbon dioxide into it. It occurs in all living organisms. Photosynthesis involves utilisation of carbon dioxide from the air and release of oxygen into the air.

Hence, carbon dioxide is replenished by the process of respiration and oxygen is replenished by the process of photosynthesis.

Properties of Air

• Air is transparent.
• It is colourless. It is not visible.
• It can be felt when it moves. Moving air is called as wind.
• Air occupies space. Air is present everywhere.
• It can be displaced by water.
• Air exerts pressure.
• It can be compressed and filled into a container.

Activity 3

Objective: To show that a gas bottle which appears to be empty to us is actually filled with air.
Materials Required: An empty bottle and a bucket with water.

• Take an empty glass bottle. Turn it, upside down in a vessel of water.
• Now, dip the open mouth of the bottle into the bucket filled with water as shown in the figure (a) above. Observe the bottle.
• Now tilt the bottle slightly and observe again.

Observation: The water does not enter into the glass bottle because the bottle is filled with air. On tilting the bottle held in water, air present in the bottle goes out in the form of air bubbles. As the air from the bottle escapes, water starts entering the glass bottle.
Conclusion: A glass bottle appears to be empty to us in actually filled with air.

Other Uses of Air:

• Air is used to rotate wind mills, which can lift water.
• Wind energy is a renewable form of energy.
• It is also used to rotate wind mills which can generate electrical energy by aerogenerators.
• It is used in sail boats.
• It helps to scatter the seeds and pollens of flowers.
• It is used to inflate the tyres of vehicles.
• Nitrogen of air is used to manufacture fertilizers.
• Air is also used for winnowing.
• Birds, insects and bats can fly due to the presence of air.
• Air present in water supports aquatic life of various plants and animals. Similarly, air present in soil supports the survival of several organisms living in it.

Activity 4

Objective: To prove that fresh water contains dissolved air.
Materials Required: A glass beaker, a tripod stand and water.
Procedure:

• Take some water in a glass vessel or beaker.
• Heat it slowly on tripod stand.
• Well before the water begins to boil, look carefully at the inner surface of the vessel. Do you see tiny bubbles on the inside?
• These bubbles come from the air dissolved in water. When you heat the water, the air dissolved in it escapes. As you continue heating, the water itself turns into vapour and finally begins to boil.

Observation: We see the bubbles of air rising up in water.
Conclusions: The air dissolves slowly in fresh water. When the water is warmed, the solubility of air decreases and it comes out of water in the form of bubbles. Hence, water contains dissolved air.

Activity 5

Objective: To show that soil contains trapped air.
Materials Required: Glass beaker, a sample of soil.
Procedure:

• Take a lump of dry soil in a beaker or a glass.
• Add water to it and note what happens.

Observation:
When the water is poured on the lump of soil, it displaces the air which is seen in the form of bubbles.
Conclusion: Soil contains air trapped between its particles.

### Class 6 Science Chapter 15 Air Around Us Additional Important Questions and Answers

Question 1.
What is the source of carbon dioxide in the air?
Respiration by animals and plants and burning of fuels.

Question 2.
Mention one necessary condition for the combustion to take place.
Presence of air.

Question 3.
Why is air considered as a mixture?
Air contains oxygen and nitrogen as its major constituents of air. These gases retain their properties in air. So the air is called a mixture.

Question 4.
Name the major gas present in the (a) inhaled air (b) exhaled air.
a. Oxygen
b. Carbon dioxide.

Question 5.
Name the major component of air.
Nitrogen gas.

Question 6.
What is the source of oxygen gas in air?
Photosynthesis by green plants is the source of oxygen gas in air.

Question 7.
What is the percentage of nitrogen in air?
78.1%.

Question 8.
What is the percentage of oxygen in air?
20.9%.

Question 9.
Name a device which uses wind energy to generate electricity.
Windmills use the wind energy to convert wind energy into electrical energy.

Question 10.
Carbon dioxide is present to the extent of only 0.03% by volume in air. Why then is it considered to be so important?
Air contains very little carbon dioxide – only 0.03%. However, it is a very crucial component of air as it is required by plants to make their food.

Question 11.
What is humidity?
The amount of water vapour present in the air is known as humidity.

Question 1.
Write four properties of air.
Properties of air:

• Air is invisible.
• Air occupies space.
• Air is transparent and colourless.
• Air exerts pressure.

Question 2.
During an incident of fire, one is advised to wrap a woollen blanket over a burning object. Explain why?
During an incident of fire, one is advised to wrap a woollen blanket over a burning object because air gaps in woollen blanket act as an insulating medium which cuts the supply of oxygen to the object that is burning, thereby prevent it from further burning.

Question 3.
What is wind energy? Write its two advantages.
Wind energy is a form of renewable energy produced through machines that use movement of wind as their power source.

1. Wind is a free and infinite resource.
2. Wind is a clean energy source.

Question 4.
What are the activities which can be possible only in the presence of air?
Activities which can be possible only in the presence of air are:

• Photosynthesis
• Burning
• Respiration
• Generation of electricity by windmills
• Sailing of ship
• Seed dispersal

Question 5.
What happens if the percentage of carbon-dioxide increases in the air?
The increased percentage of carbon- dioxide will cause green house effect, i.e., it will not allow the hot rays of sun to escape from the atmosphere, after reflection, once they enter. It will lead to global warming.

Question 6.
Why do we see the sky and air clear and clean after rainfall?
This is because the dust particles which remain suspended in air get loaded and come down on the ground due to rainfall. This is the reason that the sky and the air look clean and clear after rainfall.

Question 7.
Explain why mountaineers carry oxygen cylinders with them?
As you go up above the sea-level, the atmospheric pressure goes on decreasing and the amount of oxygen also decreases at higher altitude.

Question 8.
What is the importance of the ozone layer in the atmosphere?
The upper atmosphere contains a layer of gas called ozone. It prevents harmful rays of the sun from reaching the earth. These rays, called ultraviolet rays, can cause eye problems and skin cancer.

Question 9.
How do fish breathe?
Fishes breath in oxygen dissolved in water. Fishes have organs called gills that help to use oxygen dissolved in the water.

Question 10.
How is nitrogen obtained by plants?
Nitrogen is required by plants for their growth. But plants are not able to absorb the nitrogen directly from the air. Nitrogen in the air is brought to the earth in the form of nitric acid through lightning and rain. Microbes in soil change it to nitrate compounds which are absorbed by the plants. Also, nitrogen in the air is used by us to manufacture fertilisers. These fertilisers again provide the essential nitrogen to plants.

Question 1.
How do you prove that air occupies space?
The following activity proves that air occupies space.
Take an empty glass bottle. Turn it upside down. Now, dip the open mouth of the bottle into the bucket filled with water. Water does not enter the bottle. Now tilt the bottle slightly. Now water enters the bottle and we see bubbles coming out of the bottle.

The bottle was not empty at all. In fact, it was filled completely with air even when we turned it upside down. That is why water does not enter the bottle when it is in an inverted position, as there was no space for air to escape. When the bottle was tilted, the air was able to come out in the form of bubbles and water filled up the empty space that the air has occupied.

Question 2.
How does the atmosphere help to maintain the right temperature on the earth?
The atmosphere helps to maintain the right temperature on the earth. The heat and light of the sun fall on the earth’s atmosphere. Some of it is absorbed by the atmosphere, while the rest is reflected back. This prevents the earth from becoming very hot during the day. At night, the trapped heat in the atmosphere prevents the earth from cooling down too much. The atmosphere, thus, acts like a blanket around the earth and helps to keep the earth’s surface at the right temperature for life to exist.

Question 3.
Define pollution. How does air get polluted?
The addition of unwanted substances in the environment in quantities that are harmful to living beings is called pollution. Air is getting polluted day by day because of various human activities as given below:
a. Burning of fuels like coal and petroleum. Excessive burning of fuels like wood, smoke, etc.
b. Harmful gases released from industries.
c. Smoke released by vehicles and machines releasing gases are the major causes of air pollution. These gases spread and mix in the air and spoil the quality if air, thereby making it impure.

Question 4.
List the uses of air.
Question
Besides breathing, air is useful to us in many other ways.

• The wind makes windmills rotate. The windmills are used to draw water from tube wells and run flour mills. They are now being widely used to generate electricity.
• Aeroplanes, helicopters, balloons, parachutes and yachts work because of air.
• Birds, insects and bats are able to fly because of the presence of air.
• Air helps in the dispersal of seeds.
• Air helps in pollination of several flowers.
• Air plays an important role in the water cycle.

Question 5.
Demonstrate through a simple experiment that the air mainly contains nitrogen and oxygen in the volume ratio of 4 : 1.
Aim of experiment: To show that air contains nitrogen and oxygen in the ratio 4 : 1 by volume:

Procedure: Take a glass container and fix a candle at its centre. Put some quantity of water in the container. Place an empty, dry gas jar over it. Mark five marks above water surface on the jar at equal distances.

The candle is lightened and is covered with the gas jar. After some time, the candle is extinguished and the water level is raised in gas jar. The raised level in water is 1/5 of the volume of air in the gas jar. This proves that one part of the air of the jar is a gas which supports combustion, i.e., oxygen. Hence, 1/5 by volume is oxygen in air. Rest in mainly nitrogen.

Picture-Based Questions

Question 1.
a. What does the following pie chart represent?

b. Which gas forms the major part of the chart?