He =

(a)  

Li

(a)  

Be

(a)  

B

(a)  

C

(a)  

N

(a)  

O

(a)  

F

(a)  

Ne

(a)  

Na

(a)  

K

(a)  

Rb

(a)  

Cs

(a)  

Mg

(a)  

Ca

(a)  

Sr

(a)  

Ba

(a)  

Ra

(a)  

Al

(a)  

Ga

(a)  

Si

(a)  

P

(a)  

S

(a)  

Cl

(a)  

Br

(a)  

I

(a)  

Ar

(a)  

Kr

(a)  

Fe

(a)