Symbols of the periodic table

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Across
  1. 2. is C on the periodic table
  2. 4. is H20 on the periodic table
  3. 6. is an O on the periodic table
  4. 7. is NI on the periodic table
  5. 8. is HE on the periodic table
Down
  1. 1. the N symbol on the periodic table
  2. 3. is CH2 on the periodic table
  3. 5. is H2 on the periodic table