- AAtmosphere is the envelope of air that surrounds the earth.
- BAtmospheric gases contain nitrogen and oxygen.
- ✓Both the above are correct.
- DNone of these.
50 questions · auto-graded multiple-choice test.


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S.No.
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Column $-I$
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S.No.
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Column $-II$
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$A.$
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Oxygen.
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$(p)$
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Consumed by plants and animals during photosynthesis.
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$B.$
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Carbon dioxide.
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$(q)$
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Produced by animals during respiration.
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$C.$
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Atmosphere.
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$(r)$
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Animals that live under water.
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$D.$
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Aquatic animals.
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$(s)$
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Thin layer of air that surrounds the earth.
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$(i)$
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Respiration
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$(ii)$
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Combustion
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$(iii)$
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Burning
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Air is essential for respiration, combustion and burning.

During photosynthesis in plants, oxygen is released which is taken in by human beings and animals for respiration. They in turn release carbon dioxide needed for photosynthesis by plants.

Air is not a pure substance. A pure substance refers to an element or a compound and not a mixture. Air is a homogeneous mixture.
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S.No.
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Column$-I$
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S.No.
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Column$-II$
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$a.$
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Aquatic animals
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$1.$
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Sail boat
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$b.$
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Mountaineers
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$2.$
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Soot and dust
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$c.$
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Factories
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$3.$
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Oxygen cylinders
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$d.$
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Wind
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$4.$
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Dissolved oxygen
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$(i)$
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Tyres
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$(ii)$
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Sprayers
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$(iii)$
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Gas cylinders
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Compressed air is used for filling inflating tyres, sprayers and gas cylinders.
During respiration in animals, oxygen is taken in and carbon dioxide is released. During photosynthesis in plants, carbon dioxide is absorbed and oxygen is released. The proportion of oxygen and carbon dioxide in the atmosphere is maintained both by plants and animals.