Page 3 - COMPOSITION AND PROPERTIES OF AIR
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3.  CARBON DIOXIDE:

                      Plants need carbon dioxide to prepare their own food by the process of
                       photosynthesis. All animals directly or indirectly depend on plants for
                       food.
                      Carbon dioxide is a very small (only 0.03% by volume) component of air
                       and is a by-product of respiration by humans and animals.

                      Fire also uses up oxygen to burn and then produces carbon dioxide and
                       a few other gases upon burning. This is why we feel suffocated if there
                       is something burning inside a room. This happens due to an excess of
                       carbon dioxide as the fire continues to burn in the room, choking out
                       oxygen in the air.


                  4.  OTHER GASES:

                     Air also contains other gases such as argon, neon, hydrogen and helium.
                     Argon is used in making light bulbs and fluorescent tubes.

                  5.  Water Vapour:


                      Air contains water vapour which helps maintain the water cycle. Water
                       vapour is formed due to the evaporation of water from different water
                       bodies such as rivers, lakes and seas. When air comes in contact with
                       cold surfaces, it is these vapours that turn into or condense into
                       droplets of water.

                       The amount of water vapours in the air from place to place and time
                       to time is known as humidity.
                      Places close to coastal areas have more humidity than places away from
                       the sea. Similarly, air has more humidity during the rainy season than
                       during the summer season.

                  6.  DUST AND SMOKE:

                      Smoke  is  another  component  given  out  when  fire  burns.  It  is  very
                       harmful and adds fine dust particles and a few other gases to the air.
                       This is why industries use long chimneys in order to release this smoke
                       in the air. But as we know this act is what contributes to air pollution in

                       the environment.
                      Air  also  contains  very  fine  dust  particles  which  can  be  seen  when  a
                       beam of light enters a dark room. The tiny particles flying around in the
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