1. When we breathe which of the following gases do we use?   Oxygen   Hydrogen   Helium   Carbon Dioxide   Hint Half-n-half Clue   2. A hygroscopic substance is one which   Releases air   Absorbs water   Absorbs air   Releases water   Half-n-half Clue   3. On burning charcoal which of the following gases is produced?   Carbon Dioxide   Oxygen   Nitrous Oxide   Hydrogen   Half-n-half Clue   4. Air is   A Mixture   An Alloy   A Compound   An Element   Half-n-half Clue   5. Nitrogen constitutes nearly __ % of the atmosphere.   57   21   42   79   Half-n-half Clue   6. What gas is evolved when HCl is poured on marble chips?   Hydrogen Peroxide   Carbon Dioxide   Hydrogen   Calcium Carbonate   Half-n-half Clue   7. When hydrogen peroxide acts on Manganese Dioxide, oxygen is produced.   True   False