18
Explanation:
The family number 18 consists of a pool of elements that are less likely to enter into chemical reactions. They are called noble gases or inert gases. 
They do not react with other elements. 
  These elements are: 
          Helium 
           Neon 
          Argon
          Krypton
          Xenon
          Radon
- inert gases do not react because their outermost shell is completely filled. 
- most elements combines in order to fill their outermost shell completely
- for noble gases, this is completely done already
- all atoms on the periodic table tends to mimic them when they go into chemical reactions. 
learn more: 
Noble gas brainly.com/question/1781595
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C is the answer because water and carbon dioxide are left over after and
mitochondria is the thing in the cell that converts everything.
        
             
        
        
        
A cell is the basic unit of all life.