This could be two answers Water or Oxygen. I would go with water because it contains oxygen therefore making it a possible answer. Hope I helped. :)  
        
                    
             
        
        
        
It can impact its physical characteristics
        
             
        
        
        
Atoms are the most basic units
Elements are specific types of atoms
Compounds are composed of more than one type of element and are held together by chemical bonds
 
        
             
        
        
        
I believe the answer is c
        
                    
             
        
        
        
Answer:
Your 100% Correct Im an advanced scientist in highschool!
Well Done! Also Im new so sorry if you done trust.
Explanation: