Class X

Mass of atmosphere contained in troposphere is about
  1. 10-20%
  2. 75-80%
  3. 90-100%
  4. 50-60%
Solvents used for cleaning electronic circuit boards are
  1. chlorofluorocarbons
  2. carbons
  3. fluorides
  4. grease
Layer which protects earth from being hit by meteoroids is
  1. Troposphere
  2. Mesosphere
  3. Thermosphere
  4. Stratosphere
Reformation of ozone in stratosphere is powered by
  1. UV radiation
  2. atmospheric oxygen
  3. sunlight
  4. heat
Ozone gas (O3) has
  1. pleasant odor
  2. unpleasant odor
  3. no odor
  4. orange color
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