Basic General knowledge

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Across
  1. 2. number of chambers in human heart.
  2. 4. is also known as the Red planet.
  3. 5. driver of a train called?
  4. 8. is in the largest proportion in the earth's atmosphere
Down
  1. 1. group of stars
  2. 3. first element in the periodic table of elements.
  3. 6. bird depicts the symbol of peace.
  4. 7. largest continent in the world.