10

1234567
Across
  1. 2. - Radioactive element.
  2. 3. - Heavy noble gas.
  3. 6. - Inert gas.
  4. 7. - Cleans water.
Down
  1. 1. - Noble gas in lights.
  2. 4. - Glows in signs.
  3. 5. - Radioactive noble gas.