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Theory:

Nitrogen was first discovered by a Scottish chemist, Daniel Rutherford. By placing the burning candle in an inverted bell jar, he removed oxygen and converted it into carbon-di-oxide.
 
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Lighted candle covered with a glass jar
 
Then, he passed the remaining carbon-di-oxide through lime water to remove it.
Test for carbon-di-oxide in the air:
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Lime water test
  1. Some lime water is poured into a glass tumbler.
  2. Air is blown into the solution through a straw.
  3. After a few minutes, a white precipitate is produced in the lime water, turning it into a milky white solution.
  4. This milky white solution shows the presence of carbon-di-oxide in the air.
Test for nitrogen:
After removing the carbon-di-oxide, neither a candle burned nor a plant breathed. This test confirmed that the remaining air neither contained oxygen nor carbon-di-oxide in it. The gas that remained was named ‘nitrogen’.
 
Use of nitrogen:
1. Nitrogen is used in the food packaging industry as it keeps the food fresh.
 
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Potato chips packet
 
2. It also helps in the growth of plants and other living beings.
 
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Growth of plants
Dry ice:
Carbon-di-oxide gas, when cooled to \(-570\ ^{o}C\), directly changes to solid without changing to its liquid state. The solid carbon-di-oxide is known as dry ice.
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Dry ice
 
Use of dry ice:
It is a good refrigerating agent. It is mainly used in trucks or freight cars for refrigerating meat and fish while transporting them.
Reference:
https://upload.wikimedia.org/wikipedia/commons/b/b5/Dry_Ice_3.jpg