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differences [2marks]

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Question 12 Marks
Give points of differences : Pure air and Polluted air.
Answer
  Pure air   Polluted air
$1.$ Pure air is free from disease causing microbes and harmful pollutant gases. $1.$ Polluted air has smoke, dust and other particles, sometimes smog also.
$2.$ It has 78 % nitrogen, 21% oxygen and other gases in very small quantities such as carbon dioxide, methane, argon, ozone and water vapour. $2.$ Oxygen content is less in polluted air and other polluted gases such as oxides of nitrogen and sulphur also present.
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Question 22 Marks
Give points of differences : $CNG$ and $CFC$s
Answer
  $CNG$   $CFC$s
$1.$ Full name of $CNG$ is Compressed Natural Gas. $1.$ Full name of $CFC$s is chlorofluoro-carbons.
$2.$ It is used as a clean: fuel in vehicles and in industries. $2.$ It is used in refrigerators, air conditioners and aerosol sprays.
$3.$ it is not a pollutant. $3.$ It is a pollutant which damages ozone layer.
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differences [2marks] - Science STD 8 Questions - Vidyadip