d

  1. Hydrogen H

  2. Helium He

  3. Lithium Li

  4. Beryllium Be

  5. Boron B

  6. Carbon C

  7. Nitrogen N

  8. Oxygen O

  9. Fluorine F

  10. Neon Ne

  11. Sodium Na

  12. Magnesium Mg

  13. Aluminum Al

  14. Silicon Si

  15. Phosphorus P

  16. Sulfur S

  17. Chlorine Cl

  18. Argon Ar

  19. Potassium K

  20. Calcium Ca