1) An odorless, invisible gas that makes about 20%-22% of the earth's atmosphere is known as a. oxygen b. nitrogen c. argon d. carbon
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2) A thin layer that is held in place by gravity and provides us with oxygen is known as a. temperature b. season c. atmosphere d. weather
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3) The percentage composition of nitrogen in air is a. 58% b. 68% c. 78% d. 88%
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4) The second step of fractional distillation is heating the mixture so that components evaporate at their a. boiling point b. freezing point c. neutral point d. none of them
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5) In respiration, living organisms take in oxygen and give out a. water vapor b. argon c. carbon dioxide d. nitrogen
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6) The left over gas after the process of combustion is generally a. oxygen b. argon c. nitrogen d. carbon dioxide
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7) The sphere that prevent the ultraviolet rays from sun is known as a. exosphere b. troposphere c. atmosphere d. stratosphere
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8) In humid areas, the water vapor content is a. higher b. lower c. constant d. none of them
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9) The percentage composition of oxygen in air is a. 21% b. 31% c. 41% d. 51%
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10) Air is important on earth because it has necessary components essential for the life of a. plants b. animals c. organism d. plants, animals and other organisms
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