Chapter 15 Air Around Us

  • Air is found everywhere on the Earth and is essential part of our life.
  • Air the mixture of gases like oxygen, carbon dioxide, nitrogen and many other gases present in the small quantities.
  • Birds can fly due to the presence of air.
  • We can feel air but we cannot see it.
  • As we go higher to the mountains or the higher altitudes, we need oxygen cylinders because as we go on the high altitudes, the level of oxygen decreases.
  • The things surrounding us i.e. living and non- living together makes an environment.
  • Air is necessary for the process of burning also.
  • Carbon dioxide is released on burning which accumulates suffocation.
  • Plants inhale and animals exhales carbon dioxide during the process of respiration.
  • Oxygen is colorless, odorless and is necessary for living organisms for the process of respiration.
  • Nitrogen gas formed the major part of the air, it does not supports burning.
  • With the help of air, windmill rotates, it is used to draw water from the tube wells to generate electricity.

Download pdf of NCERT Solutions for Class Science Chapter 15 Air Around Us

Download pdf of NCERT Examplar with Solutions for Class Science Chapter 15 Air Around Us

Exercise 1 ( Page No. : 154 )

  • Q1 What is the composition of air?
    Ans:

    Air contains 21% of oxygen, 78% nitrogen, 0.03% carbon dioxide other gases like argon, dust particles, water vapours present in 0.01% quantity. Oxygen gas is very necessary for the respiration of organisms. Oxygen helps in burning; nitrogen gas is present in the large amount but it cannot help in burning process.


    Q2 Which gas in the atmosphere is essential for respiration?
    Ans:

    Oxygen gas is essential for the respiration in the environment or atmosphere. In respiration, oxidation of food is involved. We inhale oxygen and exhales carbon dioxide. If there is no oxygen, there will be no life on the Earth.


    Q3 How will you prove that air supports burning?
    Ans:

    Air supports burning. This can be proved by an experiment.

         burning experiment

    1. Take two burning candles.
    2. Put one of the burning candles inside the inverted glass.
    3. After sometime you will see that the candle which is outside, is still burning.
    4. The candle which is below the inverted glass is extinguished because of lack of oxygen there.

    This shows that air supports burning process.

    Vacuum is a place where air is absent.


    Q4 How will you show that air is dissolved in water?
    Ans:

    A lump of cotton wool shrink in water because cotton wool absorbs water and due to absorption of water the air inside the cotton wool is driven out by water. That’s why cotton wool shrinks in water.

            cotton experiment


    Q5 Why does a lump of cotton wool shrink in water?
    Ans:

    Air is dissolved in water and this can be showed by an experiment.

    Diagram:

    1. Take water in a tumbler or any other utensil.
    2. Heat it, till the vapours appear.
    3. After getting much heat, you will see that the water starts boiling.
    4. Now you can see so many bubbles are there in water.
    5. These all are air bubbles.

    This proves that air dissolves in water.


    Q6 The layer of air around the earth is known as ___________.
    Ans:

    Atmosphere

    Atmosphere may be defined as the layer of gases which contains oxygen, carbon dioxide, nitrogen and many other gases; dust particles and water vapours that are present around earth.


    Q7 The component of air used by green plants to make their food, is ___________.
    Ans:

    Carbon dioxide

    Green plant use carbon dioxide to prepare food for their own, which they get from the environment. Human beings exhales carbon dioxide and which is then is used by plants.


    Q8 List five activities that are possible due to the presence of air.
    Ans:

    The activities which are possible due to the presence of air.

    1. Respiration: Inhalation of oxygen and exhalation of carbon dioxide, this process called respiration which can be done only in the presence of air.
    2. Oxidation: All oxidation processes is proceeded in the presence of air.
    3. Combustion: For combustion oxygen is required which is present in air.
    4. Transpiration: Loss of water occurs due to presence of air.
    5. Evaporation and condensation, flying of birds are some of other activities which are possible only in the presence of air.

    Q9 How do plants and animals help each other in the exchange of gases in the atmosphere?
    Ans:

    Animals breaths out carbon dioxide. This carbon dioxide can be used by plants to prepare their food, this process is called photosynthesis which makes the balance on earth. Animals and plants by exchange of gases help each other to survive.