Answer:
answer A has four valence electrons
Explanation:
The outer shell has 4 electrons, which are considered the valence electrons 
 
        
             
        
        
        
        
Valence electrons are the electrons in the outermost shell of an element on the periodic table. Atoms want to be able to have a full outer shell and they can share or trade electrons in order to achieve this. Valence electrons are also super super important in chemical reactions. The number of valence electrons determines what group that specific atom or element is in on the periodic table. This affects the reactivity of the element.
 
        
             
        
        
        
Answer: <u>The respiratory system </u>
Explanation: It includes the nose, mouth, throat, voice box, windpipe, and lungs. Air enters the respiratory system through the nose or the mouth.
 
        
             
        
        
        
Helium has more protons making it heavier by one atomic mass.