Periodic Table

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Across
  1. 2. First element on the periodic table
  2. 3. Atomic mass of Hydrogen
  3. 4. He on the periodic table
  4. 5. Atomic mass of Helium
Down
  1. 1. Number of protons in Helium
  2. 2. Second element on the periodic table
  3. 3. Number of protons in Hydrogen
  4. 4. H on the periodic table