Answer:
I believe it is B,fluorine to complete the octet rule
Explanation:
 
        
                    
             
        
        
        
 
elements:
calcium : for strong bones
Iron : maintaining haemoglobin for metabolism
compunds
sodium chloride : to maintain blood pressure and other life processes
Adenosine Triphosphate: for metabolism, to maintain rate of inhalation and exhalation of oxygen and to supply energy
Mixture:
I) gasoline : used as fuel 
ii) cement : used in construction
 
 
        
                    
             
        
        
        
<h2>Question:</h2>
A precipitate is a solid that sometimes forms when two liquids combine.
<h2>Answer:</h2>
<u>A</u><u>.</u><u> </u><u>True</u><u> </u>
<h2>Explanation:</h2>
- <u>Because</u><u> </u><u>the</u><u> </u><u>Precipitate</u><u> </u><u>it's</u><u> </u><u>forms</u><u> </u><u>solid</u><u> </u><u>when</u><u> </u><u>two</u><u> </u><u>liquids</u><u> </u><u>combine</u><u> </u><u>to</u><u> </u><u>precipitate</u><u>.</u><u> </u>
<h2><u>#CARRYONLEARNING</u><u> </u></h2><h2><u>#STUDYWELL</u><u> </u></h2>