Periodic table crossword

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Across
  1. 2. Number of electrons in the outermost shell is _______ number(5)
  2. 5. An important element in bones present in group II(7)
  3. 8. Changing the number of neutrons in an element(7)
  4. 11. Most abundant gas in the earth's atmosphere(8)
  5. 12. Period II,Group II(9)
  6. 13. Inert gas used to make bright city lights(4)
  7. 14. Father of periodic table(9)
  8. 16. A metal used in foils(9)
  9. 17. The most common element in the universe(8)
  10. 19. Smallest part of an element(4)
  11. 20. The first alkali metal(7)
  12. 21. A liquid metal that was used in thermometers(7)
Down
  1. 1. Alkali metal in table salt(6)
  2. 3. Number of electrons present in the outermost shell(7)
  3. 4. Element used to make computer chips(7)
  4. 6. The first inert gas(6)
  5. 7. Halogen present in toothpastes(8)
  6. 9. The element we need to breathe(6)
  7. 10. Framed the law of triads(9)
  8. 15. The element diamonds are made from(6)
  9. 18. Part of an atom that has no charge(7)