Is this impossible?

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Across
  1. 2. a way to say "dummy"
  2. 3. alternate way to say "billion"
  3. 5. wardrobe in American
  4. 6. most popular food
  5. 8. anger intensification
  6. 12. the element that is named by a state
  7. 15. strongest shape
  8. 16. another word for "urticaria"
  9. 17. the smallest thing in the universe
  10. 21. hardest instrument
  11. 22. fruit with most water
  12. 23. slash but backwards
  13. 25. the favorite American icecream flavor
  14. 26. USA is #1 in this
  15. 28. doughnut muffins
  16. 29. the most essential element
  17. 31. weakest force
  18. 34. famous food Belgium made
  19. 35. fastest thing in the universe
  20. 36. starts with p and ends with orn
  21. 37. an ancient way to tell time
Down
  1. 1. the person you're going to fight
  2. 4. a shape with 10 sides
  3. 6. the most radioactive element
  4. 7. opposite of questionable
  5. 9. give
  6. 10. salt
  7. 11. whatever this is _
  8. 13. the process of removing salt from water
  9. 14. between the chest and the hips
  10. 18. opposite of intelligent
  11. 19. used as energy
  12. 20. 3.26 light years
  13. 24. extra
  14. 27. cutaneous condition
  15. 30. Earth's favorite color
  16. 32. rarest element
  17. 33. opposite of permanent
  18. 34. a long, deep body of water that reaches far inland