1. Air is   A Mixture   An Element   A Compound   An Alloy   Hint Half-n-half Clue   2. Which gas in the atmosphere saves us from the UV rays of the sun?   Ozone   Carbon Monoxide   Nitrogen   Oxygen   Half-n-half Clue   3. Nitrogen constitutes nearly __ % of the atmosphere.   57   42   21   79   Half-n-half Clue   4. On burning charcoal which of the following gases is produced?   Hydrogen   Nitrous Oxide   Carbon Dioxide   Oxygen   Half-n-half Clue   5. When we breathe which of the following gases do we use?   Oxygen   Carbon Dioxide   Helium   Hydrogen   Half-n-half Clue   6. A hygroscopic substance is one which   Absorbs air   Releases air   Absorbs water   Releases water   Half-n-half Clue   7. Dry ice is   Solid Carbon Dioxide   Ice with salt added   Very Cold Ice   Any Frozen Liquid   Half-n-half Clue