The reaction between hydrogen (H2) and fluorine (F2) is given below,
                                   H2 + F2 ---> 2HF
One mole of both hydrogen and fluorine yields to 2 moles of hydrogen fluoride. This can also be expressed as, 2 grams of hydrogen and 38 grams of fluorine will form 40 grams of hydrogen fluoride. From the given, only 20 grams of HF is formed with 19 g of it being fluorine. Thus, the percentage fluorine of the compound formed is 95%. 
        
                    
             
        
        
        
I would say A but then again im not too sure so hope that makes it easier to somehow
        
                    
             
        
        
        
Hello there.
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Some elementary particles are positively or negatively 
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b. charged particles. 
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No. The only thing that changed was the looks of the gasoline, not the chemical components.