Answer:
From molar mass=total RAM of each individual element
78.8=(16+1)×3+M
78.8-51=M
27.8g/mol=M
 
        
             
        
        
        
Lithium i believe is the answer
        
             
        
        
        
Answer:
Nitrogen atom is small in size than phosphorus thus the bond between its nucleus and valence electrons are stronger than phosphorus.
Hope it helps...。◕‿◕。
 
        
             
        
        
        
Answer: A and D, I believe
Explanation:
 
        
                    
             
        
        
        
Answer:
5 atoms 
Explanation:
According to the law of conservation of mass, "matter is neither created nor destroyed in the cause of a chemical reaction". 
We finish with what we start with in a chemical reaction. Although new species might form, the number of atoms on both sides of the expression will still be maintained. 
All chemical reactions obey this law of conservation.