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Give one uses of each, , Argon— Argon is filled into electric bulbs to, , prevent the oxidation of their filaments., , Helium-— It is used in filling up weather, , observation balloons., , Neon— Neon is used for making, , advertisement sign boards., , Radon-— It is used for treatment of Cancer., , Krypton— It is used in photography., , Xenon-— It is also used in photography.

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Answer the question put against the, , following constituents of air:, , Nitrogen : Explain its significance for, , plants and animals., , Plants convert nitrogen into protein. It is an, important constituent of proteins, which, are necessary for the growth of animals,, plants and human beings. Plants convert, , nitrogen into proteins., , Oxygen : What is the percentage, , proportion of oxygen in air ? Why is oxygen, , called active air., , 20.9%, oxygen is called active air because, it supports life on earth. It is essential for, , the process of combustion.

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C), , Carbon dioxide : “Although carbon dioxide, plays no role in respiration, all life would, come to an end if there is no carbon, dioxide in air.” Support this statement with, , relevant facts., , Carbon dioxide is essential for, photosynthesis by which green plants, prepare their food. It minimises heat loss, by radiation. Thus, it balances the, , temperature on earth., , Water vapours : Explain their role in, , modifying the earth's climate., , Water vapour determine the earth's climate, conditions. It causes rain. It controls the, , rate of evaporation from the bodies of

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plants and animals., , 3) Define the term pollutants., , Pollutants : Air contains substances which, are harmful to plants and animals. These, , harmful substances are called pollutants., , b) acid Rain, , Acid rain : When sulphur trioxide and, nitrogen oxide present in the air mix with, rainwater they form sulphuric acid and, nitric acid respectively. Rainwater, , containing these acids is called acid rain.

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C) Global warming, , Global warming : An increase in the, percentage of carbon dioxide, methane,, nitrous oxide and chlorofluorocarbon traps, the heat causing the temperature of the, earth and its surroundings to rise. This is, , known as global warming., , d) smog, , Smog: Oxides of nitrogen form a mixture, of smoke and fog known as smog which, , affects our eyes too., , “Air is a mixture”. Support this statement, , citing at least three evidences., , “Air is a mixture” The following are in