Topic outline

    • Air Around us

      Q39. Write four properties of the air.

      Ans. Properties of the air

                                  i.        Air is invisible.

                                 ii.        Air occupies space.

                                iii.        Air is transparent.

                                iv.        Air has no color.


      Q40. During an incident of fire, one is advised to wrap a woolen blanket over a burning object. Explain why?

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


      Q41. How will you show that air is dissolved in water?

      Ans. Take some water in a glass vessel or beaker. Heat it slowly on a tripod stand. Well before the water begins to boil, we see tiny bubbles at the inner surface of the vessel. These bubbles come from the air dissolved in water. This proves that air is dissolved in water.

      Q42. How do organisms living under the soil get air for respiration?

      Ans. The organisms which are living under the soil such as in the roots of a plant respire by taking oxygen present in the soil. Some organisms make deep burrows and holes in the soil through which the air reaches them for respiration.


      Q43. Why do living things need air to survive?

      Ans. Living things cannot survive without air. We breathe in oxygen and breathe out Carbon Dioxide. Through a process called photosynthesis, plants extract carbon dioxide from the air and use it to produce energy. They release oxygen in the air in this process. Thus air is important for all living things.


      Q44. What is wind energy? Write its two advantages.

      Ans. Wind energy is a form of renewable energy produced through machines that uses movement of wind as their power source.

      Two advantages

                                i.        Wind is a free and infinite resource.

                               ii.        Wind is a clean energy source.

      Q45.  Prove that 'Air contains dust and smoke’.

      Ans. 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. We see some tiny shining particles moving in the beam of sunlight. This shows that air also contains dust particles.

      Q46. What are the major constituents of air and their percentages?

      Ans. The major constituents of air and their percentages are:

      Nitrogen – 78.09%

      Oxygen – 20.95%

      Argon - 0.93%

      Carbon dioxide - 0.04%

      Air also contains other gases, water vapor and dust particle.


      Q47. What are the activities which can be possible only in the presence of air?

      Ans. Activities which can be possible only in the presence of air are:

                                i.        Photosynthesis

                               ii.        Burning

                              iii.        Respiration

                              iv.        Generation of electricity by windmills

                              v.        Sailing of ship

                             vi.        Seed dispersal

      Q48. How balance of oxygen and carbon dioxide in the atmosphere is maintained?

      Ans. During photosynthesis plant uses carbon dioxide and releases oxygen. Plants also consume oxygen for respiration, but they produce more of it than they consume. Oxygen in air is used by living organism present in air, water or soil during respiration. This shows the interdependence of plants and animals and thus the balance of oxygen and carbon dioxide in the atmosphere is maintained.


      Q49. Draw a diagram showing composition of air in atmosphere.


      Q50. How do you prove air occupies space?

      Ans. 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.

      This activity shows that air occupies space.


      Q51. How will you demonstrate that air mainly contains oxygen and nitrogen?

      Ans. We can show that air mainly contains oxygen and nitrogen from the following experiment.

      Fix two small candles of the same size in the middle of two shallow containers. Now, fill the containers with some water. Light the candles and then cover each one of them with an inverted glass. When most of this oxygen is used up by the burning candle, it can no longer burn and blows out. Also, some of the space occupied by the oxygen inside the glass becomes empty and the water rises up to fill or occupy this space.

      A major part of air is still present in the glass bottle even after the candle blew out. This indicates the presence of some component in the air, which does not support burning. The major part of air (which does not support burning candle) is nitrogen. It takes up nearly four-fifth of the space that air fills.

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