He → (a)  

Li → (a)  

Be → (a)  

B → (a)  

C → (a)  

N → (a)  

O → (a)  

F → (a)  

Ne → (a)  

Na → (a)  

Mg → (a)  

Al → (a)  

Si → (a)  

P → (a)  

S → (a)  

Cl → (a)  

Ar → (a)  

K → (a)  

Ca → (a)  

Fe → (a)  

Co → (a)  

Ni → (a)  

Cu → (a)  

Zn → (a)  

Ag → (a)  

Au → (a)  

Hg → (a)  

Pb → (a)  

Sn → (a)  

31. Cr → (a)  

32. Mn → (a)  

33. Br → (a)  

34. I → (a)  

35. Pt → (a)  

36. U → (a)  

37. Se → (a)  

38. Ti → (a)  

39. Ra → (a)  

40. Xe → (a)  

1. Hydrogen → (a)  

2. Helium → (a)  

3. Lithium → (a)  

4. Beryllium → (a)  

5. Boron → (a)  

6. Carbon → (a)  

7. Nitrogen → (a)  

8. Oxygen → (a)  

9. Fluorine → (a)  

10. Neon → (a)  

11. Sodium → (a)  

12. Magnesium → (a)  

13. Aluminum → (a)  

14. Silicon → (a)  

15. Phosphorus → (a)  

16. Sulfur → (a)  

17. Chlorine → (a)  

18. Argon → (a)  

19. Potassium → (a)  

20. Calcium → (a)  

21. Iron → (a)  

22. Cobalt → (a)  

23. Nickel → (a)  

24. Copper → (a)  

25. Zinc → (a)  

26. Silver → (a)  

27. Gold → (a)  

28. Mercury → (a)  

29. Lead → (a)  

30. Tin → (a)  

31. Chromium → (a)  

32. Manganese → (a)  

33. Bromine → (a)  

34. Iodine → (a)  

35. Platinum → (a)  

36. Uranium → (a)  

37. Selenium → (a)  

38. Titanium → (a)  

39. Radium → (a)  

40. Xenon → (a)